Slashing Telecoms Costs: Why UK Businesses Are Moving to Microsoft Teams Direct Routing via SIP
Over 90% of UK organisations rely on Microsoft Teams every single day to chat, collaborate, and host internal video meetings. Yet, when it comes to making external calls to clients, suppliers, or mobile devices, many companies find themselves stuck in a dual setup.
They are either paying way too much for Microsoft’s native Calling Plans or running a separate legacy phone system alongside Teams. That means paying double for lines, extra maintenance, and user licenses you just don’t need.
With the UK PSTN and ISDN copper switch-off deadline fast approaching, hanging onto legacy telephony is no longer a viable option. But there’s a straightforward fix: Microsoft Teams Direct Routing powered by high-performance SIP Trunking.
Here is how replacing native Microsoft Calling Plans with SIP-backed Direct Routing unlocks proper enterprise-grade calling, keeps your existing numbers intact, and knocks 30% to 50% off your monthly voice bill.
What is Microsoft Teams Direct Routing?
Out of the box, Microsoft Teams is built mainly for internal collaboration. To call external landlines and mobiles, Teams needs a connection to a real-world phone network.
Direct Routing acts as the secure bridge between Microsoft Teams and an external specialist telecommunications provider. Using a certified Session Border Controller (SBC), Direct Routing lets you connect high-speed SIP Trunks straight into your Teams app.
[ Microsoft Teams Client ]
│
▼ (SIP Protocol)
[ Certified Session Border Controller (SBC) ]
│
▼
[ Silver Lining Voice Network & SIP Trunks ] ──► [ External PSTN / Mobile Networks ]
Instead of buying rigid, expensive monthly call packages directly from Microsoft, Direct Routing lets you “Bring Your Own Carrier” (BYOC). That gives you total control over your call rates, routing rules, and underlying voice setup.
Microsoft Calling Plans vs. SIP Direct Routing: How They Compare
For a small team of two or three people, a basic Microsoft Calling Plan might do the job. But for growing mid-sized businesses and multi-site UK companies, those costs stack up fast.
| Feature / Metric | Microsoft Native Calling Plans | SIP Direct Routing (Managed Provider) |
| Pricing Model | Expensive per-user, per-month bundled licenses (£12 to £18+ per user) | Flexibly priced SIP trunks with aggressive volume usage rates |
| Potential Savings | Baseline pricing; gets costly fast for medium-to-large teams | 30% to 50% average reduction in total voice spend |
| Legacy PBX Integration | None (Forces a pure cloud migration) | Hybrid ready (Connects Teams to existing PBX, door entry, or lift lines) |
| Call Routing Control | Basic, out-of-the-box routing options | Advanced custom routing, IVRs, and queue management |
| Number Porting | Rigid process with limited UK geographic support | Full, managed number porting across all UK area codes |
| Disaster Recovery | Relies entirely on Microsoft uptime | Automatic failover to mobile or secondary locations via SIP |
4 Reasons UK Businesses Are Switching to SIP Direct Routing
1. Significant Cost Reduction at Scale
Microsoft Calling Plans charge a flat fee per user each month, whether that person makes one call or 100. If you have 100 employees, you are stuck paying for 100 individual calling plans.
With SIP Direct Routing, you only pay for the call capacity (channels) and actual usage your business needs. Because SIP trunks share call capacity across your entire organisation, mid-sized companies regularly cut their overall phone bill by up to 50% while getting far better rates for national and international calls.
2. Preparing for the UK PSTN/ISDN Switch-Off
Openreach is steadily switching off the UK’s old copper and ISDN line network, meaning remaining legacy lines face price hikes and an eventual blackout.
Direct Routing gives you a clean way to modernise your voice setup using future-proof SIP trunking. If your business relies on specialised hardware like physical desk phones, contact centre software, or analogue lines, Direct Routing serves as a great hybrid bridge. You can bring those legacy setups straight into Teams without disrupting daily business.
3. Proper Contact Centre Features
Standard Microsoft Teams lacks some of the advanced call-handling tools required by busy customer service desks, sales teams, and contact centres.
By layering SIP Direct Routing over Teams, you open up key enterprise feature sets:
- Call Recording & Compliance: Effortlessly record and store calls to stay compliant with PCI DSS, GDPR, or FCA regulations.
- Omnichannel & Wallboards: Link inbound call queues directly to live agent dashboards and wallboards.
- Automated Failover: If an office loses internet access, the SIP network automatically reroutes incoming calls to mobile phones or backup locations within seconds.
4. Keep Your Existing Numbers
Changing phone numbers is a nightmare for customer trust and brand recognition. With a managed SIP Direct Routing rollout, your existing UK geographic (01/02), non-geographic (03), and freephone (0800) numbers are smoothly ported to Microsoft Teams. Your staff log into Teams just like they do every day, but now they have a full dial pad ready to reach clients anywhere.
How to Deploy Direct Routing in 4 Simple Steps
1. Voice Audit & Network Assessment: Prerequisite Phase.
Review your current Microsoft 365 licenses (such as the Teams Phone Standard add-on or E5), calculate your typical call volume, and map out all phone numbers that need to be ported.
2. Session Border Controller (SBC) Configuration:
Set up a certified SBC (cloud-hosted or on-site) to securely route incoming and outgoing SIP traffic between your network and Microsoft’s cloud servers.
3. SIP Trunk Provisioning & Number Porting:
Set up flexible SIP channels with negotiated rates for UK and international calls. Port your main corporate numbers over to the new SIP trunks with zero downtime.
4. Teams Admin Centre Voice Routing & User Testing:
Configure your voice routing policies in the Microsoft Teams Admin Centre, run a quick pilot test with a small group, and roll it out to the rest of the team.
Stop Paying Premium Rates for Microsoft Calling
Connecting your business phone system into Microsoft Teams should not mean overpaying for rigid, per-user calling plans. By leveraging high-capacity SIP Direct Routing, your business gets lower call rates, full PSTN switch-off readiness, and a reliable corporate voice platform, all inside the Teams app your staff already use every day.
Need help migrating your voice setup? Give Silver Lining Convergence a call on 0345 683 11 11 or speak with our voice team to get a free SIP Direct Routing cost audit for your business.