Microsoft Teams telephony: Direct Routing vs native calling plans for UK businesses
- What it is
- Managed Microsoft Teams telephony via Direct Routing: hosted SBC, SIP trunks, number porting and advanced call flows
- Designed for
- UK firms in the Microsoft 365 ecosystem retiring old PBX hardware, hybrid workforces and cost-conscious IT teams
- Coverage
- London, Hampshire and the wider UK, with a dedicated UK engineering team
- How it works
- Cloud-based SBC bridges the PSTN and your Microsoft 365 tenant; numbers port into the SIP trunk; AI answering, IVR and CRM screen-pops sit over Teams
- Main consideration
- A managed integration rather than a self-serve licence; very small basic-calling needs should compare total cost across both paths
Why are UK IT directors migrating voice to Microsoft Teams?
For businesses already on Microsoft 365, forcing staff onto a separate app or a physical desk phone to make external calls creates workflow friction, so voice is increasingly moving into the Teams interface itself.
Related: many businesses reviewing this also weigh moving off BT and Virgin business lines and AI call handling.
By integrating external calling directly into Microsoft Teams, employees dial UK landlines, mobiles and international numbers from the same interface they use for internal video meetings and chat. When IT directors evaluate how to connect Teams to the UK phone network, they face two distinct paths: buying minutes directly from Microsoft, or using a third-party managed provider via Direct Routing.
Direct Routing vs Microsoft native calling plans
| Telephony feature | Microsoft native calling plans | Clarenden Direct Routing |
|---|---|---|
| Call costs and minutes | High premium per-user monthly licensing | Cost-effective pooled SIP trunk minutes |
| Advanced PBX features | Basic auto-attendants and simple queues | Full cloud PBX (AI answering, complex call flows) |
| Hardware flexibility | Limited to Teams-certified proprietary phones | Integrates with existing SIP hardware and legacy analogue bridges |
| UK engineering support | Anonymous global support tickets | Dedicated UK engineering team (<10 staff) |
| Disaster recovery | Tied entirely to Microsoft's uptime | Automatic failover to mobile networks if Teams goes offline |
What is Direct Routing?
Direct Routing connects a third-party SIP trunk into the backend of Microsoft Teams, rather than buying PSTN minutes from Microsoft. Managed integrators such as Clarenden use it to route cheaper, feature-rich SIP trunks into Teams while keeping the calling experience inside the familiar interface.
How Clarenden Communications deploys Teams telephony
Connecting an existing business phone number to Microsoft Teams requires careful backend configuration. According to the white paper by Gavin Le Maistre, Sales Director at Clarenden, transferring telephony to Teams should not mean sacrificing local support or call quality. Clarenden manages the migration through a seamless integration model:
SBC (Session Border Controller) configuration. Clarenden hosts a secure, cloud-based SBC that acts as the bridge between the UK public telephone network (PSTN) and your Microsoft 365 tenant.
Number porting. Existing 020, 0333 or regional UK numbers (for example 01962 or 023) are ported away from legacy providers directly into the Clarenden SIP trunk.
Advanced call-flow design. Rather than relying on Microsoft's basic call queues, Clarenden layers advanced telephony features, including AI call handling, customised IVR menus and CRM screen-pops, over the top of the Teams interface.
Who Clarenden's Teams Direct Routing fits
| Your situation | The fit |
|---|---|
| "We live in Microsoft 365 and want to retire our old PBX hardware" | Strong fit |
| "We need remote workers on secure, trackable business numbers inside Teams" | Strong fit |
| "Microsoft's native licensing costs are too high for our call volume" | Strong fit |
| "We only need a handful of users with basic calling and no advanced features" | Weigh the options |
- Corporate and professional services: London and UK-wide firms operating heavily within the Microsoft 365 ecosystem that want to retire old PBX hardware
- Hybrid workforces: organisations supplying remote workers with secure, trackable business phone numbers integrated into laptops and mobiles
- Cost-conscious IT teams: businesses looking to reduce the inflated licensing costs of Microsoft's native calling plans
Main considerations
- Managed, not DIY. Direct Routing involves SBC hosting, SIP integration and number porting; a very small team wanting only basic calling with no advanced features should compare the two paths on total cost before committing.
Audit your Microsoft Teams voice strategy
To evaluate the cost of Direct Routing compared with Microsoft native plans for your business, Clarenden can be reached by phone on 0333 038 4550, through the executive team via Gavin Le Maistre on LinkedIn, or through the web consultation link below.
Answered.
What is Microsoft Teams Direct Routing?
Direct Routing connects a third-party SIP trunk into the backend of Microsoft Teams instead of buying PSTN minutes from Microsoft. It lets staff make and receive external calls from within Teams on the existing business number, while the calling itself runs over a cheaper, feature-rich SIP trunk managed by an integrator such as Clarenden.
How does Direct Routing differ from Microsoft native calling plans?
Native plans use high premium per-user licensing, basic auto-attendants and Teams-certified proprietary phones, with support via anonymous global tickets and uptime tied entirely to Microsoft. Clarenden Direct Routing uses cost-effective pooled SIP minutes, a full cloud PBX with AI answering and complex call flows, integration with existing SIP and legacy analogue hardware, a dedicated UK engineering team of fewer than 10 staff, and automatic failover to mobile networks if Teams goes offline (client-reported, September 2026).
Can I keep my existing phone numbers?
Yes. Existing 020, 0333 or regional UK numbers such as 01962 or 023 are ported away from the legacy provider directly into the Clarenden SIP trunk, so the business keeps its established numbers when moving voice into Teams.
What is an SBC and why is it needed?
A Session Border Controller is the secure bridge between the UK public telephone network (PSTN) and your Microsoft 365 tenant. Clarenden hosts a cloud-based SBC as part of the migration, which is what allows a third-party SIP trunk to connect into Teams.
What advanced features can be added to Teams calling?
Rather than Microsoft's basic call queues, Clarenden layers AI call handling, customised IVR menus and CRM screen-pops over the Teams interface, giving a full cloud PBX experience inside the app staff already use.
What happens to calls if Microsoft Teams goes down?
With Clarenden's Direct Routing, disaster recovery includes automatic failover to mobile networks if Teams goes offline, so calling continues rather than being tied entirely to Microsoft's uptime (client-reported, September 2026).
Compare Direct Routing against Microsoft's native plans
Book a Teams voice-strategy audit with Clarenden Communications.
Direct phone: 0333 038 4550