For UK businesses already embedded in the Microsoft 365 ecosystem, the prospect of making and receiving telephone calls directly within Microsoft Teams is enormously appealing. Rather than maintaining a separate telephony platform alongside your collaboration tools, Teams direct routing UK allows you to connect your existing PSTN connectivity — or a new hosted PBX platform — directly into the Teams client, giving every user a single interface for chat, video, and voice calls to any telephone number in the world.
But the path from "we want to make calls in Teams" to a fully operational, enterprise-grade voice deployment is rarely straightforward. Microsoft offers multiple approaches — Calling Plans, Operator Connect, and Direct Routing — each with different cost profiles, flexibility trade-offs, and technical requirements. Layered on top are questions about Session Border Controllers, cloud PBX architecture, IP phone system compatibility, licensing tiers, call quality optimisation, and the rapidly evolving UK provider landscape following the full PSTN switch-off.
This guide is written specifically for UK IT decision-makers and managed service provider clients who need a thorough, jargon-decoded walkthrough of every Teams voice option. We cover the complete journey: from understanding the architectural differences between each approach, through SBC deployment and configuration, to handset selection, business mobile VoIP integration, licensing costs, and real-world deployment timelines. Whether you are a 20-person firm in Birmingham or a 2,000-seat enterprise across multiple UK sites, by the end of this article you will have a clear framework for choosing and implementing the right Teams voice strategy.
The convergence of telephony and collaboration is not a future trend — it is happening right now across UK organisations of every size. With BT's PSTN and ISDN networks fully decommissioned, every business must route voice traffic over IP. For the millions of UK workers who already spend their day inside Microsoft Teams, the logical next step is to eliminate the separate phone system entirely and handle all voice communications within the same platform they use for messaging, meetings, and document collaboration. The question is not whether to do it, but how to do it well.
Understanding Microsoft Teams Voice: The Three Approaches
Microsoft provides three distinct methods for enabling PSTN calling within Teams. Each occupies a different position on the spectrum between simplicity and flexibility, and understanding their fundamental differences is the essential first step before making any procurement decisions.
Microsoft Calling Plans
Microsoft Calling Plans are the simplest option. Microsoft acts as both your telephony platform and your PSTN carrier. You purchase a Calling Plan licence for each user, Microsoft assigns a phone number (or ports your existing numbers), and calls are routed entirely through Microsoft's own telephony infrastructure. There is no additional hardware to deploy, no SBC to configure, and no third-party carrier relationship to manage.
For small UK businesses with straightforward telephony needs — perhaps 10 to 50 users who need a DDI number and basic inbound/outbound calling — Calling Plans offer the fastest path to Teams voice. You can be live within days, and the entire system is managed through the Teams admin centre.
The limitations become apparent at scale. Microsoft's UK calling plan pricing sits at approximately £6–£10 per user per month for domestic calling (with international plans costing more), but this only includes a limited number of minutes. High-volume callers or businesses with significant outbound activity can quickly exceed the included allowance, triggering overage charges. Number porting from some UK carriers can be slow. Geographic number availability is inconsistent — if you need numbers for specific UK area codes, Microsoft may not have them in stock. And you are entirely dependent on Microsoft's PSTN infrastructure for call quality and reliability, with limited ability to troubleshoot or influence routing decisions.
Operator Connect
Operator Connect is Microsoft's middle-ground option, introduced to address the inflexibility of Calling Plans without requiring the technical complexity of Direct Routing. With Operator Connect, you choose from a list of Microsoft-certified telecommunications operators (including several UK providers like BT, Gamma, and Virgin Media Business) who integrate their PSTN connectivity directly into the Teams admin centre.
The experience is smoother than Direct Routing: your chosen operator appears in the Teams admin portal, you can assign numbers and manage calling policies through a unified interface, and the operator handles the SBC infrastructure on their side. You benefit from the operator's UK network coverage, geographic number ranges, and potentially more competitive per-minute rates than Microsoft's own Calling Plans.
The trade-off is that you are limited to the operators Microsoft has certified for the UK market. If your preferred carrier or hosted PBX provider is not on the Operator Connect list, this option is not available to you. You also have less granular control over call routing, failover behaviour, and integration with legacy telephony systems compared to Direct Routing.
Teams Direct Routing
Teams direct routing UK is the most flexible and powerful option, and it is the approach most medium and large UK businesses ultimately adopt. Direct Routing allows you to connect virtually any PSTN carrier, SIP trunk provider, or cloud PBX platform to Microsoft Teams via a certified Session Border Controller (SBC). You retain full control over your carrier relationships, call routing logic, number management, and failover architecture.
This flexibility comes with additional complexity. You need an SBC (either a physical appliance or a virtual/cloud-hosted instance), SIP trunk connectivity from a UK carrier, appropriate Microsoft licensing, and the technical expertise to configure and maintain the integration. For many UK businesses, this is where a managed service provider like Cloudswitched becomes invaluable — handling the SBC deployment, carrier integration, and ongoing management so the business gets the benefits of Direct Routing without needing in-house telephony engineering expertise.
Microsoft Calling Plans
Operator Connect
Direct Routing
Many UK businesses start with Microsoft Calling Plans for a small pilot group, then migrate to Direct Routing once they have validated that Teams voice meets their needs. This staged approach reduces risk and allows your team to build familiarity with Teams telephony before committing to the SBC infrastructure investment.
Hosted PBX vs Cloud PBX: Clearing Up the Terminology
Before diving deeper into Teams Direct Routing, it is worth addressing a source of persistent confusion in the UK telecommunications market: the difference (or lack thereof) between a hosted PBX and a cloud PBX. These two terms are frequently used interchangeably by providers, yet there are nuanced distinctions that matter when you are planning a Teams integration.
Hosted PBX Defined
A hosted PBX is a telephone system where the PBX (Private Branch Exchange) hardware and software reside at your provider's data centre rather than on your business premises. Your desk phones and softphones connect to this remote PBX over the internet, and the provider handles all maintenance, updates, and redundancy. The "hosted" in the name refers to the fact that a specific, dedicated PBX instance is running on the provider's infrastructure on your behalf.
In a traditional hosted PBX model, your provider might allocate a specific server or virtual machine to your organisation's PBX instance. This gives you a degree of isolation and customisation — your PBX configuration, dial plans, and call routing rules are independent of other customers on the same platform. Many UK hosted PBX providers offer extensive configuration options, integration with CRM systems, bespoke IVR menus, and detailed call analytics.
Cloud PBX Defined
A cloud PBX typically refers to a multi-tenant telephony platform delivered as a service. Rather than having a dedicated PBX instance, your organisation is one of many tenants on a shared, scalable cloud infrastructure. The provider manages the underlying platform, and you access your telephony features through a web portal, API, or client application.
Microsoft's own telephony capability within Teams is, architecturally, a cloud PBX. When you enable Teams voice (via any of the three methods), Microsoft's cloud infrastructure acts as your PBX — handling call routing, voicemail, auto-attendants, call queues, and all the features you would expect from a business telephone system. The key difference is that this PBX is tightly integrated into the Teams collaboration platform rather than being a standalone telephony service.
Why It Matters for Teams Direct Routing
When you deploy Teams direct routing UK, Teams itself becomes your cloud PBX, replacing whatever separate hosted or on-premises PBX you were previously using. The SBC and SIP trunk provide the connection to the public telephone network, but all PBX functionality — call handling, voicemail, auto-attendants, call queues, call park, music on hold — is delivered by the Teams platform.
However, some organisations choose a hybrid approach: keeping their existing hosted PBX for certain functions (such as analogue fax lines, lift phones, or door entry systems) while routing the majority of user calls through Teams via Direct Routing. The SBC sits at the intersection, intelligently directing traffic between Teams, the hosted PBX, and the PSTN based on configurable routing rules.
| Characteristic | Hosted PBX | Cloud PBX (Teams) | Hybrid (Both) |
|---|---|---|---|
| Infrastructure location | Provider's data centre | Microsoft Azure global network | Both |
| Multi-tenancy | Often single-tenant per customer | Fully multi-tenant | Mixed |
| Integration with Teams | Separate platform, possible CTI | Native — calls within Teams client | Teams for users, PBX for legacy |
| Analogue device support | Yes, via ATAs | No native support | Yes, via hosted PBX |
| Customisation depth | Extensive dial plans, IVR | Microsoft feature set only | Maximum flexibility |
| Typical UK cost per user | £8–£18/month | £2–£8/month (plus M365 licence) | £6–£14/month blended |
| Ideal for | Voice-centric businesses | M365-embedded organisations | Complex estates, phased migration |
If your organisation has analogue devices (fax machines, franking machines, door entry intercoms, or lift emergency phones), do not assume they can move to Teams. These devices almost always need a traditional hosted PBX or an analogue telephone adapter connected to a SIP trunk. Plan your hybrid architecture early to avoid a last-minute scramble during migration.
Session Border Controllers: The Heart of Direct Routing
The Session Border Controller (SBC) is the critical piece of infrastructure that makes Teams direct routing UK possible. It sits at the boundary between Microsoft's cloud and your SIP trunk provider, translating protocols, securing the connection, and managing call routing decisions. Understanding SBC options is essential for any business planning a Direct Routing deployment.
What an SBC Does
An SBC performs several vital functions in a Direct Routing deployment. It terminates the SIP trunk from your PSTN carrier on one side and connects to Microsoft Teams via a TLS-encrypted SIP connection on the other. It handles protocol translation between the carrier's SIP dialect and Microsoft's specific SIP requirements. It provides security by acting as a firewall for voice traffic, preventing toll fraud, denial-of-service attacks, and unauthorised call routing. It manages media transcoding when codecs differ between the carrier and Teams. And it applies call routing rules, directing calls to the appropriate destination based on number patterns, time of day, user location, or failover conditions.
SBC Deployment Options
UK businesses have three main SBC deployment models, each suited to different scales and operational preferences.
Physical SBC appliance: A dedicated hardware device installed in your server room or data centre. Vendors like AudioCodes, Ribbon Communications (formerly GENBAND/Sonus), and Oracle offer Microsoft-certified SBC appliances ranging from small units handling 10 concurrent calls to enterprise devices supporting thousands. Physical SBCs offer the highest performance and lowest latency, but require rack space, power, and on-site maintenance.
Virtual SBC: The same SBC software running as a virtual machine on your existing virtualisation platform (VMware, Hyper-V) or in a UK data centre. Virtual SBCs offer the same feature set as physical appliances with the added flexibility of virtual infrastructure — easier backups, snapshots, and disaster recovery. Most UK managed service providers deploy virtual SBCs for their clients.
Cloud-hosted SBC (SBC as a Service): A fully managed SBC running in a cloud environment (Azure, AWS, or the provider's own infrastructure). You do not manage the SBC at all — the provider handles deployment, configuration, patching, and monitoring. This is the most popular option for UK SMEs using Direct Routing, as it eliminates the operational overhead entirely. Providers like Cloudswitched offer managed SBC services where the entire Direct Routing infrastructure is handled as a turnkey solution.
Microsoft-Certified SBC Vendors for the UK Market
Microsoft maintains a list of certified SBC vendors whose products have been tested and validated for Direct Routing interoperability. For UK deployments, the most commonly encountered certified SBCs include:
| Vendor | Model / Platform | Deployment Type | Typical UK Price Range | Concurrent Call Capacity |
|---|---|---|---|---|
| AudioCodes | Mediant VE / CE / Physical | All three options | £1,200–£15,000+ | 10–10,000+ |
| Ribbon Communications | SBC SWe Edge / SBC 1000/2000 | Virtual / Physical | £2,000–£20,000+ | 25–10,000+ |
| Oracle | Enterprise SBC / AP Series | Physical / Virtual | £5,000–£30,000+ | 100–50,000+ |
| TE-SYSTEMS | anynode | Virtual / Cloud | £500–£5,000 | 5–500+ |
| Metaswitch | Perimeta SBC | Virtual / Cloud | £3,000–£12,000 | 50–5,000+ |
SBC Configuration Essentials
Configuring an SBC for Teams direct routing UK involves several critical steps. The SBC must be paired with your Microsoft 365 tenant using a valid TLS certificate from a trusted public Certificate Authority — Microsoft does not accept self-signed certificates. The SBC's FQDN (fully qualified domain name) must be registered in your DNS and added to your Teams Direct Routing configuration via the Teams admin centre or PowerShell.
SIP trunk configuration on the carrier-facing side involves defining the SIP peer (your carrier's SBC or proxy), codec preferences (G.711 for quality, G.729 for bandwidth efficiency), DTMF relay method (RFC 2833 is standard), and caller ID handling rules. On the Teams-facing side, you configure the SIP profile for Microsoft's specific requirements, including the use of the sip.pstnhub.microsoft.com domain for signalling and the appropriate media bypass settings.
Call routing rules are configured on the SBC to direct traffic appropriately. Inbound calls from the PSTN are routed to Teams users based on the called number. Outbound calls from Teams users are routed to the SIP trunk based on the dialled number pattern. Emergency calls (999/112) must be routed with particular care, ensuring they reach the correct UK emergency services gateway with accurate location information.
Step 1: Prerequisites and Planning
Confirm Microsoft 365 licensing (Teams Phone licences), select SBC vendor and deployment model, choose SIP trunk provider, document number ranges and call routing requirements. Allow 1–2 weeks.
Step 2: SBC Deployment
Deploy the SBC (physical, virtual, or cloud-hosted). Obtain and install a TLS certificate from a public CA. Configure DNS records for the SBC's FQDN. Allow 3–5 days.
Step 3: Microsoft Tenant Configuration
Register the SBC in the Teams admin centre. Configure voice routing policies, PSTN usage records, and voice routes. Assign Teams Phone licences to pilot users. Allow 2–3 days.
Step 4: SIP Trunk Integration
Configure the SIP trunk on the SBC. Establish peering with the carrier. Test inbound and outbound call flow, codec negotiation, and DTMF. Allow 3–5 days.
Step 5: Pilot Testing
Assign numbers to a small group of pilot users. Test all call scenarios: inbound, outbound, transfer, hold, conference, voicemail, emergency (using test numbers). Validate call quality metrics. Allow 1–2 weeks.
Step 6: Number Porting and Migration
Submit number porting requests to move existing DDI ranges from the legacy carrier. Coordinate porting dates with zero-downtime cutover planning. Allow 2–4 weeks (carrier-dependent).
Step 7: Full Rollout and Optimisation
Migrate all users to Teams voice. Configure auto-attendants, call queues, and holiday schedules. Enable call analytics and quality monitoring. Decommission legacy PBX. Allow 2–4 weeks.
Microsoft Teams Licensing for Voice: A UK Cost Breakdown
Licensing is one of the most frequently misunderstood aspects of Teams voice deployments. The telephony capability in Teams is not included in standard Microsoft 365 subscriptions — you need additional licences, and the correct combination depends on which voice approach you choose. Here is a clear breakdown of what UK businesses need.
Foundation: Microsoft 365 Subscription
Every user who will make or receive PSTN calls through Teams needs a Microsoft 365 subscription that includes Teams. This can be Microsoft 365 Business Basic, Business Standard, Business Premium, E3, E5, or the equivalent frontline worker plans. The subscription provides the Teams application itself, but not the telephony capability.
Teams Phone Licence (Formerly Phone System)
The Teams Phone licence (previously branded as "Phone System") adds PBX capabilities to Teams: the ability to make and receive PSTN calls, voicemail, auto-attendants, call queues, call park, and other telephony features. This licence is included in Microsoft 365 E5 and Microsoft 365 Business Premium. For all other plans, it must be purchased as an add-on at approximately £6.60 per user per month in the UK.
PSTN Connectivity (Varies by Approach)
On top of the Teams Phone licence, you need a method for connecting to the public telephone network. This is where the three approaches diverge in cost:
| Component | Calling Plans | Operator Connect | Direct Routing |
|---|---|---|---|
| M365 subscription (per user/mo) | £9.40–£32.40 | £9.40–£32.40 | £9.40–£32.40 |
| Teams Phone licence (per user/mo) | £6.60 (or included in E5) | £6.60 (or included in E5) | £6.60 (or included in E5) |
| PSTN connectivity (per user/mo) | £6.00–£10.00 (Calling Plan) | £3.00–£7.00 (operator-dependent) | £1.50–£4.00 (SIP trunk share) |
| SBC infrastructure (per user/mo) | N/A | N/A | £0.50–£2.00 (amortised) |
| Total voice add-on cost | £12.60–£16.60 | £9.60–£13.60 | £8.60–£12.60 |
The cost advantage of Direct Routing becomes more pronounced at scale. For a 200-user UK business, the annual saving compared to Calling Plans can be £9,600–£19,200 — comfortably covering the cost of a managed SBC service and SIP trunk provision with money to spare.
Common Licence (Teams Phone with Calling Plan)
For organisations that prefer the simplicity of Calling Plans but want to avoid purchasing licences piecemeal, Microsoft offers the "Teams Phone with Calling Plan" bundle at approximately £12.60 per user per month. This combines the Teams Phone licence and a domestic Calling Plan into a single SKU, simplifying procurement for smaller organisations. However, for UK businesses processing more than 1,200 domestic minutes per user per month, overages can quickly erode the cost advantage.
Resource Accounts and Service Numbers
Auto-attendants and call queues in Teams require "resource accounts" — essentially virtual user accounts that are assigned phone numbers but do not represent real people. These resource accounts need a free Microsoft Teams Phone Resource Account licence. If the resource account needs a service number (such as a main office number or contact centre queue number), you may also need a Calling Plan licence or to assign the number via Direct Routing.
If your organisation already has Microsoft 365 E5 licences, the Teams Phone capability is included at no additional cost. The only extra expense for Direct Routing is the SIP trunk and SBC infrastructure — potentially as little as £2–£4 per user per month. This makes E5 organisations the best candidates for rapid Teams voice deployment with maximum cost efficiency.
IP Phone System Compatibility with Microsoft Teams
While many organisations embrace software-based calling through the Teams desktop and mobile apps, a significant proportion of UK businesses still need physical desk phones. Reception desks, warehouse offices, common areas, and executive offices often require dedicated handsets. The good news is that the IP phone system ecosystem for Teams has matured considerably, with a wide range of Microsoft-certified devices available.
Teams-Certified IP Phones
Microsoft certifies specific IP phone models for use with Teams, ensuring they meet quality, feature, and security standards. Certified phones run a native Teams application (not just a SIP client) and provide access to Teams-specific features including presence indicators, calendar integration, voicemail visual notification, and one-touch meeting join.
The major vendors producing Teams-certified IP phones for the UK market include:
Yealink — The dominant vendor in the UK Teams phone market. Their T-series (T53, T54W, T56A, T58A) and MP-series (MP54, MP56, MP58) offer a range of price points from basic desk phones to executive models with large colour touch screens and Bluetooth connectivity. Yealink also produces the CP935P conference phone and A20/A30 Teams-certified collaboration bars.
Poly (now HP) — The CCX series (CCX400, CCX500, CCX600, CCX700) is popular in the UK enterprise market. Poly phones are known for excellent audio quality (their HD Voice heritage) and robust build quality. The CCX700 with its large touch screen is a popular choice for executive offices.
AudioCodes — The C-series (C435HD, C448HD, C450HD, C455HD) offers competitive pricing and solid Teams integration. AudioCodes is particularly popular in managed service provider environments due to their bulk management tools and consistent firmware update cadence.
Crestron — Focused on the premium conference room market rather than individual desk phones. Their Teams-certified room systems integrate IP telephony with video conferencing, room scheduling, and AV control.
| Phone Model | Type | Display | Key Features | UK Price (ex. VAT) |
|---|---|---|---|---|
| Yealink MP54 | Desk phone | 4" colour touch | Teams native, USB-C, PoE, Wi-Fi optional | £165–£195 |
| Yealink MP58 | Executive desk | 7" colour touch | Teams native, Bluetooth 5.0, USB-C, Wi-Fi | £280–£340 |
| Poly CCX500 | Desk phone | 5" colour touch | Teams native, Poly HD Voice, PoE | £220–£270 |
| Poly CCX700 | Executive desk | 7" colour touch | Teams native, HD camera option, Bluetooth | £380–£450 |
| AudioCodes C448HD | Desk phone | 7" colour touch | Teams native, GigE, PoE, USB | £195–£240 |
| Yealink CP935P | Conference phone | 4" colour touch | Teams native, 360° pickup, USB-C, Bluetooth | £320–£380 |
Using Existing SIP Phones with Teams
If your organisation has recently invested in IP phone system hardware that is not Teams-certified, you may still be able to use these devices with Direct Routing. Standard SIP phones can register to the SBC (rather than directly to Teams), and the SBC handles the translation between the phone's SIP signalling and the Teams infrastructure. This approach — sometimes called "SBC-registered endpoints" — does not provide the native Teams experience (no presence, no calendar integration), but it allows basic inbound/outbound PSTN calling through the existing handsets.
This is particularly useful during phased migrations, where you want to move users to Teams voice without immediately replacing all desk phones. Users get their calls routed through Teams, and you can plan a gradual hardware refresh over 12–24 months rather than a costly one-time replacement.
Business Mobile VoIP: Extending Teams to Every Device
The modern UK workforce is not tethered to a desk, and any credible Teams voice deployment must account for business mobile VoIP. Whether your team members are commuting between client sites, working from home, or travelling internationally, they need to make and receive business calls on their mobile devices with the same quality, features, and professional caller ID as their desk-based colleagues.
Teams Mobile App as Your Business Phone
The Microsoft Teams mobile app (available on iOS and Android) functions as a fully featured business mobile VoIP client. When a user has a Teams Phone licence and is enabled for Direct Routing, they can make and receive PSTN calls on their mobile device using their business number. Inbound calls ring on all registered devices simultaneously — desk phone, desktop app, and mobile app — and the user answers on whichever device is most convenient.
Call quality on the Teams mobile app depends heavily on the mobile device's internet connection. On a strong Wi-Fi connection, call quality is excellent — indistinguishable from a desk phone. On 4G/5G mobile data, quality is generally good but can be affected by network congestion, signal strength, and handoff between cell towers. The Teams app includes adaptive bitrate technology that adjusts codec parameters in real time to maintain call quality as network conditions change.
SIM-Based Mobile Integration
For organisations where mobile call quality over VoIP is a concern — perhaps due to remote locations with poor mobile data coverage — some UK providers offer SIM-based mobile integration. This approach uses a special SIM card (or eSIM profile) that routes calls through the mobile network's native voice infrastructure rather than over data, while still integrating with Teams for presence, call history, and voicemail.
Microsoft's own "Teams Phone Mobile" offering (formerly known as Operator Connect Mobile) enables this through partnerships with selected mobile operators. A user's mobile number becomes their Teams number, and calls are natively carried on the mobile network but appear within Teams. This eliminates the VoIP quality variability entirely, though it requires a participating mobile operator and may involve higher per-user costs.
Mobile Device Management Considerations
Deploying Teams as a business mobile VoIP solution across your workforce raises device management questions. If your organisation uses Microsoft Intune or another MDM (Mobile Device Management) solution, you can enforce policies on the Teams mobile app: requiring a PIN to access the app, preventing screenshots of confidential call information, wiping corporate data if a device is lost, and ensuring the app is kept up to date.
For businesses operating a BYOD (Bring Your Own Device) policy, Microsoft's app protection policies allow you to secure the Teams app and its data without managing the entire personal device. This is crucial for UK businesses subject to GDPR and data protection requirements — you need to ensure that business call recordings, voicemails, and contact lists stored within the Teams app are protected and can be remotely wiped if an employee leaves the organisation.
The trend is unmistakable. Three-quarters of UK professionals who have access to Teams calling on their mobile devices use it regularly for business calls. For many, the mobile app has entirely replaced their desk phone as the primary calling device, with the physical handset relegated to conference room use or reception desks. This shift has significant implications for IP phone system procurement — many organisations are now purchasing far fewer desk phones than they would have five years ago, with the saving redirected to better headsets, mobile device accessories, and network infrastructure improvements.
Call Quality: Engineering Reliable Voice Over IP
No matter how elegant your Teams Direct Routing architecture is, it counts for nothing if call quality is poor. Voice traffic is uniquely sensitive to network impairments — even minor levels of latency, jitter, or packet loss that would be imperceptible in web browsing or email can make voice calls sound garbled, robotic, or completely unintelligible. Here is how to engineer your network for reliable, high-quality voice.
Key Quality Metrics
Latency (delay): The time it takes for a voice packet to travel from the speaker to the listener. For good call quality, end-to-end latency should be below 150 milliseconds. Above 200ms, users will notice a noticeable delay, and conversations become awkward as speakers talk over each other. Microsoft recommends a maximum of 50ms network latency for optimal Teams call quality.
Jitter: The variation in latency between successive packets. Even if average latency is low, high jitter causes packets to arrive out of order, resulting in choppy or distorted audio. Jitter should be kept below 30 milliseconds, ideally below 15ms.
Packet loss: The percentage of voice packets that fail to reach the destination. Voice is particularly intolerant of packet loss because there is no time to retransmit lost packets (unlike TCP-based traffic). Packet loss above 1% causes noticeable audio degradation. Above 3%, calls become unusable. Target: below 0.5%.
MOS (Mean Opinion Score): A composite measure of call quality rated on a scale of 1 (bad) to 5 (excellent). A MOS score of 4.0 or above indicates "toll quality" voice — comparable to a traditional landline call. Teams provides MOS scores for every call in the Call Quality Dashboard, making it easy to monitor trends.
Network Optimisation for Teams Voice
Quality of Service (QoS): Configure QoS policies on your network to prioritise voice traffic. Teams voice uses specific UDP port ranges (49152–53247 for media) and DSCP markings (EF/46 for voice) that should be prioritised in your router and switch configurations. On managed networks, QoS is the single most impactful improvement you can make for call quality.
Local internet breakout: Teams voice traffic should take the most direct path to Microsoft's network. If your organisation routes internet traffic through a centralised proxy or VPN, voice packets suffer unnecessary latency. Configure split-tunnelling or local internet breakout so Teams traffic goes directly from the user's location to the nearest Microsoft edge node. Microsoft publishes the IP ranges and URLs that should be allowed direct access.
Bandwidth planning: A single Teams voice call uses approximately 60–120 Kbps in each direction (depending on codec). A 100-user office with a peak concurrent call rate of 20% needs approximately 2.4 Mbps of dedicated bandwidth for voice alone. Add video calling, screen sharing, and general internet usage, and you can see why bandwidth planning is essential. As a rule of thumb, allocate at least 100 Kbps per user for voice, plus your standard internet bandwidth requirements.
Media Bypass: Media Bypass is a Direct Routing feature that routes the actual voice media (RTP packets) directly between the Teams client and the SBC, bypassing the Microsoft cloud. This reduces latency (the media path is shorter), saves bandwidth (media does not traverse the internet to Microsoft and back), and can improve call quality significantly for on-premises users. Media Bypass requires the SBC and the Teams client to be on the same network or have direct connectivity, and the SBC must support it (most modern SBCs do).
Monitoring and Diagnostics
Microsoft provides two powerful tools for monitoring Teams call quality. The Call Quality Dashboard (CQD) provides aggregate analytics across your entire organisation — trend data on call quality, failure rates, network metrics, and device performance. The Call Analytics tool provides per-call, per-user diagnostics — drill down into a specific poor-quality call to see exactly where in the network path the problem occurred.
For UK businesses with a managed service provider like Cloudswitched, these tools are monitored proactively. Rather than waiting for users to complain about call quality, the MSP reviews CQD data regularly, identifies degradation trends before they become user-facing problems, and takes corrective action — whether that is adjusting QoS policies, upgrading a site's internet connection, or replacing a faulty network switch.
The UK Provider Landscape for Teams Direct Routing
The UK market for Teams direct routing UK services has expanded rapidly, driven by the PSTN switch-off, the surge in Microsoft 365 adoption, and the shift to hybrid working. Understanding the different types of providers and what they offer helps you make an informed choice.
Categories of UK Providers
Tier 1 — Telecommunications Carriers: Major UK carriers like BT, Gamma, Vodafone Business, and Virgin Media Business offer Direct Routing as part of their broader business telephony portfolios. They provide the SIP trunks, number ranges, and often a managed SBC service. Their strengths are network coverage, number portability, and the ability to bundle connectivity and telephony. Their weaknesses can be slower support response times, less flexible contract terms, and a tendency to push their own Operator Connect offerings over Direct Routing.
Tier 2 — Specialist VoIP / UCaaS Providers: Companies like 8x8, RingCentral, Vonage, and Dialpad offer their own UCaaS platforms but also provide Teams Direct Routing integration. They typically have well-developed self-service portals, competitive per-user pricing, and strong feature sets. However, their Direct Routing offering may be secondary to their native platform, and you may find the Teams-specific feature set less mature than a dedicated Direct Routing provider.
Tier 3 — Managed Service Providers (MSPs): IT managed service providers like Cloudswitched specialise in designing, deploying, and managing the complete Teams voice solution for their clients. They handle the SBC, the carrier relationship, the Microsoft licensing, the network assessment, and the ongoing monitoring — presenting the business with a turnkey Teams voice service. For organisations without in-house telephony expertise, an MSP provides the deepest expertise and most responsive support.
What to Look for in a UK Teams Voice Provider
Regardless of which tier of provider you choose, there are critical evaluation criteria every UK business should apply:
Microsoft partnership level: Microsoft Gold or Solutions Partner for Modern Work certification demonstrates that the provider has invested in Teams-specific training and has a track record of successful deployments. Ask about their specific Teams voice deployment count — not just general Microsoft 365 experience.
UK number coverage: Can the provider supply geographic numbers for all the UK area codes you need? Can they port your existing numbers? What is their typical porting timeline? Some providers have excellent London coverage but struggle with Scottish, Welsh, or Northern Irish area codes.
SBC management: Do they offer a fully managed SBC, or will you need to manage your own? If managed, what are the SLAs for availability and incident response? Can they support Media Bypass and Local Media Optimisation for your multi-site estate?
Support responsiveness: Telephony issues are urgent — when calls are not working, business stops. What are the provider's support SLAs specifically for voice incidents? Do they offer 24/7 support, or are you limited to business hours? Can they troubleshoot end-to-end (Microsoft tenant, SBC, carrier) or only their own infrastructure?
Emergency calling compliance: UK Ofcom regulations require that emergency calls (999/112) be routed correctly with accurate caller location information. How does the provider handle emergency calling for Teams users, particularly remote workers who may be calling from different locations? Do they support dynamic emergency calling with location-aware routing?
Advanced Features: Auto-Attendants, Call Queues, and Contact Centres
Beyond basic inbound and outbound calling, Teams provides a suite of advanced telephony features that can replace functionality previously requiring expensive third-party systems.
Auto-Attendants
Teams auto-attendants replace the traditional IVR (Interactive Voice Response) systems that greet callers with "Press 1 for Sales, Press 2 for Support." You configure auto-attendants through the Teams admin centre, defining greeting messages (recorded or text-to-speech), menu options, business hours schedules, and routing destinations. Multiple auto-attendants can be nested — a main greeting directing to department-specific sub-menus, each with their own business hours and holiday schedules.
For UK businesses, auto-attendants support multiple languages (including Welsh, if your organisation operates in Wales and needs to comply with Welsh Language Standards). You can configure different greetings and menus based on the called number, the time of day, or even the day of the year (automatically routing callers to a bank holiday message on UK public holidays).
Call Queues
Call queues distribute incoming calls to a group of agents (team members) based on configurable routing methods: round robin, serial (ring each agent in order), longest idle (ring the agent who has been waiting longest), or attendant routing (ring all agents simultaneously). Queue settings include maximum wait time, maximum queue size, music on hold, and overflow actions when the queue is full.
For a hosted PBX or cloud PBX replacement, Teams call queues cover the needs of most UK businesses. Customer service teams, help desks, and reception functions can all be handled natively within Teams without a separate call distribution platform. Agents see the queue calls in their Teams client, can manage their availability status, and supervisors can monitor queue performance through Teams reports.
Contact Centre Integration
For organisations with more sophisticated contact centre requirements — skills-based routing, screen pops, CRM integration, real-time wallboards, workforce management, and detailed agent analytics — Teams integrates with numerous third-party contact centre platforms through the Teams Connected Contact Centre certification programme. UK-relevant certified contact centre solutions include NICE CXone, Five9, Genesys Cloud, 8x8 Contact Centre, and Anywhere365.
These platforms use Teams as the agent's communication interface while providing the advanced contact centre logic, reporting, and management capabilities that Teams' native call queues cannot match. For UK businesses running formal customer service operations with more than 10–15 agents, a certified contact centre platform layered over Teams Direct Routing is typically the recommended architecture.
Compliance, Security, and UK Regulatory Requirements
Deploying voice through Teams in the UK brings specific compliance and regulatory obligations that differ from a traditional on-premises telephone system. Understanding these requirements is essential for any organisation subject to industry regulation or handling sensitive customer data.
Ofcom Compliance
UK businesses providing telephony services (even internally) must comply with Ofcom's General Conditions of Entitlement. The most relevant requirements for Teams voice deployments include: accurate provision of caller line identification (CLI), correct routing of emergency calls to the 999/112 services, compliance with number portability regulations, and ensuring calls to non-geographic numbers (0800, 0845, 0870, etc.) are correctly handled and billed.
Your Teams Direct Routing provider and SIP trunk carrier bear primary responsibility for Ofcom compliance at the network level, but your organisation must ensure that emergency calling is correctly configured for all users, including remote workers. Microsoft's dynamic emergency calling feature, combined with correct SBC configuration, can provide location-aware emergency routing — but it must be actively configured and tested.
Call Recording and GDPR
Many UK businesses are legally required to record calls — financial services firms under FCA MiFID II regulations, for example. Teams supports native call recording (stored in OneDrive or SharePoint) and integrates with third-party compliance recording solutions (such as Verint, NICE, and Dubber) for organisations needing more robust recording, archival, and retrieval capabilities.
Under GDPR and the UK Data Protection Act 2018, you must inform callers when calls are being recorded (typically via an auto-attendant greeting), have a lawful basis for recording, store recordings securely, and respond to subject access requests for call recordings within the statutory timeframe. Your data retention policies must specify how long call recordings are kept and when they are deleted.
Data Residency
Microsoft stores Teams data (including call records, voicemails, and recordings) in the data centre region associated with your Microsoft 365 tenant. For UK organisations, this is typically the UK South (London) and UK West (Cardiff) Azure regions. However, in a Direct Routing deployment, the actual voice media may traverse different paths depending on whether Media Bypass is enabled and where your SBC is located. Organisations with strict data residency requirements should ensure their SBC is hosted in the UK and that Media Bypass is configured to keep media paths domestic.
Migration Strategies: Moving from Your Existing PBX to Teams
Migrating from an existing telephone system to Teams voice is rarely an overnight affair. A well-planned migration strategy minimises disruption, manages risk, and ensures users are confident with the new system before their old phones are decommissioned.
Big Bang vs Phased Migration
A "big bang" migration — switching all users to Teams voice on a single date — is the fastest approach but carries the highest risk. If something goes wrong (a number porting delay, an SBC misconfiguration, a network issue), the entire organisation is affected. Big bang migrations are only advisable for small organisations (under 30 users) with simple telephony requirements and strong technical support available on the day.
Phased migration is the approach most UK businesses adopt. You migrate users in waves, typically starting with IT staff (who can troubleshoot their own issues), followed by less call-intensive departments, and finishing with customer-facing teams. Each phase allows you to identify and resolve issues before they affect more users. A typical phased migration for a 200-user UK business takes 4–8 weeks.
Coexistence Scenarios
During the migration period, your organisation will be running two telephony systems simultaneously. This coexistence can be managed in several ways:
Parallel running: Both the legacy PBX and Teams are active, with users assigned to one system or the other. Calls between the two systems are routed via the SBC. This is the safest approach — if a Teams user encounters issues, their calls can be quickly redirected back to the legacy PBX.
Hybrid routing: All inbound calls arrive at the SBC, which routes them to either Teams or the legacy PBX based on the called number's current assignment. This allows seamless inbound calling during migration — callers do not notice any change regardless of which system the called user is on.
Number forwarding: For organisations with particularly complex legacy PBX environments, temporary call forwarding rules can bridge the two systems. Calls to legacy PBX extensions can be forwarded to Teams numbers and vice versa. This is a simpler but less elegant solution, suitable for short transition periods.
Phase 1: Assessment and Planning (Weeks 1–2)
Audit existing telephony: number ranges, call flows, IVR menus, hunt groups, fax lines, analogue devices. Document every integration point. Assess network readiness for voice. Select SBC and carrier.
Phase 2: Infrastructure Deployment (Weeks 3–4)
Deploy and configure SBC. Establish SIP trunk. Configure Teams tenant: voice routing policies, dial plans, emergency calling. Provision Teams Phone licences. Set up auto-attendants and call queues.
Phase 3: Pilot Migration (Weeks 5–6)
Migrate IT team and selected volunteers (20–30 users). Test all call scenarios thoroughly. Gather user feedback. Refine configuration based on real-world usage. Resolve any call quality issues.
Phase 4: Staged Rollout (Weeks 7–10)
Migrate remaining departments in planned waves. Port DDI number ranges from legacy carrier. Train each department before migration. Provide hypercare support during each wave's first week.
Phase 5: Legacy Decommission (Weeks 11–12)
Verify all users are fully operational on Teams. Decommission legacy PBX. Cancel legacy carrier contracts. Complete documentation and handover. Transition to BAU support model.
Cost Analysis: Total Cost of Ownership for Teams Voice
Understanding the true cost of a Teams voice deployment requires looking beyond the per-user licensing fees. Here is a comprehensive total cost of ownership (TCO) analysis for a hypothetical 150-user UK business migrating from a traditional hosted PBX to Teams Direct Routing.
Year 1 Cost Breakdown
| Cost Component | Annual Cost | Notes |
|---|---|---|
| Microsoft 365 E3 licences (150 users) | £54,000 | £30/user/mo — already paid for email, Teams, Office |
| Teams Phone add-on licence (150 users) | £11,880 | £6.60/user/mo |
| SIP trunk (150 channels) | £5,400 | £3/user/mo including UK calling bundle |
| Managed SBC service | £3,600 | £2/user/mo for cloud-hosted, managed SBC |
| IP phone hardware (50 handsets) | £10,000 | One-time. Yealink MP54 at £200 each |
| Migration and professional services | £5,000 | One-time. SBC config, number porting, training |
| Headsets (100 USB/Bluetooth) | £6,500 | One-time. Jabra/Poly, avg £65 each |
| Year 1 Total (voice add-on only) | £42,380 | Excludes M365 licence (already paid) |
| Year 2+ Annual (voice add-on only) | £20,880 | Recurring: Phone licence + SIP + SBC |
Compare this to the cost of maintaining a separate hosted PBX alongside Microsoft 365. A typical UK hosted PBX at £22–£28 per user per month (including handset rental) costs £39,600–£50,400 per year for 150 users — and that is on top of the Microsoft 365 subscription you are already paying for email and collaboration. By consolidating telephony into Teams, you eliminate the duplicate platform cost and gain a unified user experience.
Common Pitfalls and How to Avoid Them
Having guided numerous UK businesses through Teams voice deployments, Cloudswitched has identified the most common pitfalls that derail or degrade implementations. Here is how to avoid each one.
Pitfall 1: Underestimating Network Readiness
The most frequent cause of poor Teams call quality is inadequate network infrastructure. Businesses that assume their existing internet connection and internal network will "just work" for voice are often disappointed. Voice traffic requires consistent, low-latency connectivity — something that may not have been a priority when the network was designed for email and web browsing.
Solution: Conduct a formal network readiness assessment before deploying Teams voice. Microsoft's Network Assessment tool tests bandwidth, latency, jitter, and packet loss to the nearest Microsoft edge node. Additionally, assess your internal network for potential bottlenecks: ageing switches without QoS support, wireless access points with insufficient capacity, or VPN configurations that route voice traffic unnecessarily.
Pitfall 2: Ignoring Emergency Calling Configuration
Emergency calling (999/112) requires special attention in a Teams voice deployment. Unlike a traditional PBX connected to a fixed location, Teams users can be anywhere — in the office, at home, at a client site, or on the move. If a user dials 999 and the emergency services receive incorrect location information, lives could be at risk.
Solution: Configure dynamic emergency calling in Teams, which uses network subnet, Wi-Fi BSSID, or switch port to determine the user's location and route emergency calls with accurate address information. For remote workers, configure emergency addresses based on their registered home location. Test emergency calling as part of every deployment — use the dedicated test emergency numbers provided by your carrier rather than dialling 999.
Pitfall 3: Poor User Adoption
Deploying the technology perfectly means nothing if users refuse to use it. Some employees, particularly those accustomed to traditional desk phones for decades, resist the change to software-based calling. They may perceive the new system as complicated, unreliable, or inferior to their familiar handset.
Solution: Invest in user training and change management. Demonstrate the benefits (single interface, mobile access, voicemail transcription) rather than just the mechanics. Provide high-quality headsets — poor audio equipment is the fastest way to generate negative user sentiment. Offer physical desk phones to users who genuinely need them (receptionists, common areas) rather than forcing everyone onto softphones.
Pitfall 4: Inadequate Testing Before Go-Live
Rushing from SBC configuration to production rollout without thorough testing is a recipe for trouble. Number porting issues, codec mismatches, DTMF problems (affecting automated phone menus), and unexpected call routing behaviour all emerge during testing — and they are far easier to resolve before users depend on the system.
Solution: Maintain a comprehensive test plan covering: inbound and outbound calls to UK geographic numbers, UK mobile numbers, UK non-geographic numbers (0800, 0845, 0870), international numbers, conference calls, call transfers (blind and consultative), call forwarding, voicemail deposit and retrieval, auto-attendant menu navigation, call queue distribution, DTMF mid-call (for interacting with external IVR systems), and fax (if applicable). Every scenario should be tested with both desk phones and the Teams desktop/mobile apps.
Future-Proofing Your Teams Voice Investment
The telephony landscape continues to evolve rapidly, and your Teams voice deployment should be architected to accommodate future developments without requiring a complete rebuild.
Microsoft's Ongoing Platform Development
Microsoft continues to invest heavily in Teams telephony features. Recent and forthcoming additions include: Teams Premium features (AI-powered meeting recap, custom branding for calls), Copilot integration for call summarisation and follow-up actions, improved contact centre APIs, enhanced call analytics powered by machine learning, and deeper integration with Microsoft Viva for employee experience insights.
By building on Direct Routing, you position your organisation to adopt these features as they become available. The SBC-based architecture is flexible enough to integrate with future Microsoft capabilities, third-party innovations, and new communication channels (such as Rich Communication Services) as they mature.
Multi-Channel Communication
Voice calling is increasingly just one channel in a broader customer and employee communication strategy. Teams is evolving to support SMS/MMS messaging (via third-party integrations through Direct Routing), WhatsApp Business integration, and web chat capabilities. Organisations that deploy Direct Routing with a flexible SBC architecture can add these channels incrementally without re-architecting their telephony infrastructure.
AI and Automation
Artificial intelligence is transforming business telephony. Microsoft's Copilot for Teams can transcribe calls in real time, summarise conversations, extract action items, and even draft follow-up emails based on call content. Third-party AI platforms can analyse call recordings for sentiment, compliance keywords, and customer satisfaction indicators. Teams Direct Routing provides the foundation for these capabilities — you need the calls flowing through Teams before you can apply AI analysis to them.
For UK businesses evaluating their telephony strategy, the trajectory is clear: the organisations that invest in a robust Teams voice deployment today will be best positioned to leverage AI-powered communication features as they mature over the coming years. The cloud PBX capabilities within Teams, combined with Direct Routing's flexibility, create a platform that can evolve with your business rather than constraining it.
Why UK Businesses Choose Cloudswitched for Teams Voice
Deploying Microsoft Teams as your organisation's cloud PBX is a transformative project that touches networking, telephony, Microsoft 365 administration, security, compliance, and end-user experience. Getting it right requires expertise across all these domains — and getting it wrong means disrupted communications, frustrated users, and lost business.
Cloudswitched is a London-based managed service provider specialising in Microsoft 365, cloud telephony, and IT infrastructure for UK businesses. Our Teams voice practice has delivered Direct Routing deployments for organisations ranging from 15-user professional services firms to 1,500-seat multi-site enterprises. We handle every aspect of the journey: network assessment, SBC deployment and management, carrier selection and SIP trunk provisioning, Microsoft licensing optimisation, number porting, user training, and ongoing monitoring and support.
Our approach is straightforward: we design the right architecture for your specific requirements, deploy it with meticulous attention to detail, and manage it proactively so your team can focus on their work rather than their phone system. Whether you need a simple hosted PBX replacement for a single office or a complex multi-site Direct Routing deployment with contact centre integration, legacy PBX coexistence, and business mobile VoIP for a distributed workforce, Cloudswitched has the expertise and track record to deliver it.
Frequently Asked Questions
Can I keep my existing UK phone numbers when moving to Teams?
Yes. Number porting is a standard process when migrating to Teams Direct Routing. Your existing DDI numbers, main office numbers, and freephone numbers can all be ported to your new SIP trunk provider. The porting timeline varies by carrier — typically 5–15 working days for UK geographic numbers. During the porting process, calls continue to be delivered normally, and the actual cutover is seamless from the caller's perspective.
Do I need a Teams Phone licence for every user?
Only users who need to make or receive PSTN calls require a Teams Phone licence. Users who only need Teams for internal calling (Teams-to-Teams voice and video calls within your organisation) can do so with their standard Microsoft 365 licence at no additional cost. This allows you to optimise licence spend — a 200-person organisation where only 120 users need external calling capability can save approximately £6,336 per year by not licensing the remaining 80 users for PSTN calling.
What happens to calls if the internet goes down?
This is one of the most common concerns. With Teams Direct Routing, you can configure failover scenarios on your SBC. If the connection to Microsoft Teams is lost, the SBC can redirect calls to mobile phones, an alternative PSTN destination, or a backup hosted PBX. Some SBC vendors (notably AudioCodes with their "Survivable Branch Appliance" feature) can even provide basic local calling capability during an outage, allowing users to make and receive calls through the SBC directly.
Is Teams voice suitable for contact centres?
Teams' native call queues are suitable for informal call groups and small customer service teams (up to approximately 10–15 agents). For formal contact centre operations requiring skills-based routing, real-time dashboards, recording with quality management, and workforce scheduling, you should deploy a Microsoft-certified contact centre solution that integrates with Teams. The contact centre handles the routing logic while Teams provides the agent's communication interface.
How does Teams handle fax?
Teams does not natively support fax transmission. For UK businesses that still need fax capability (common in healthcare, legal, and certain government interactions), the recommended approach is a cloud fax service (such as eFax or HelloFax) that delivers faxes as email attachments, or maintaining a single analogue fax line through your SBC connected to a physical fax machine. Most organisations find that cloud fax services are more practical and cost-effective than maintaining physical fax infrastructure.
Can remote workers use Teams voice from home?
Absolutely. This is one of the primary advantages of Teams voice. Remote workers connect to their home broadband, open the Teams desktop or mobile app, and make and receive calls exactly as they would in the office. Their business number, voicemail, and call features work identically. For optimal call quality, we recommend a wired Ethernet connection (rather than Wi-Fi), a quality USB or Bluetooth headset, and a broadband connection with at least 10 Mbps download and 2 Mbps upload speeds.
Conclusion: Making the Right Teams Voice Decision for Your UK Business
Microsoft Teams voice — whether via Calling Plans, Operator Connect, or Direct Routing — represents a genuine paradigm shift in how UK businesses handle telephony. By consolidating voice communications into the same platform your team already uses for messaging, meetings, and collaboration, you eliminate complexity, reduce costs, and create a more productive working environment.
For the majority of UK businesses with more than 30 users, Teams direct routing UK via a managed service provider delivers the optimal combination of flexibility, cost efficiency, and control. You choose your own carrier, maintain full control over call routing and number management, benefit from competitive SIP trunk pricing, and retain the freedom to integrate with legacy systems, contact centre platforms, and business mobile VoIP services.
The key to a successful deployment is thorough planning, the right technology partners, and a phased migration strategy that prioritises user experience. Whether you are replacing a legacy hosted PBX, consolidating a fragmented multi-site IP phone system, or building a greenfield cloud PBX environment, the path to Teams voice is well-trodden and the technology is mature.
The question is no longer whether Teams can handle your business telephony — it can, and it does so for millions of users worldwide. The question is whether you are getting the right guidance to implement it properly. That is where expert support makes the difference between a telephony project that transforms your business and one that creates frustration and regret.
Ready to Bring Calling Into Microsoft Teams?
Cloudswitched designs and manages Teams Direct Routing deployments for UK businesses of all sizes. From network assessment to SBC deployment, number porting to user training — we handle the entire journey so you can focus on your business. Book a free consultation to discuss your requirements.
CloudSwitched
London-based managed IT services provider offering support, cloud solutions and cybersecurity for SMEs.
