Microsoft Teams Direct Routing Service for UK Businesses

If you are weighing up how Teams telephony fits your wider voice estate, start at our business VoIP pillar, then come back here for the direct routing detail.

How does Microsoft Teams Direct Routing work?

Direct routing sits an SBC between Teams and a SIP trunk from your chosen carrier. The SBC handles call signalling, media, security and protocol translation, and Teams routes outbound calls down whichever trunk your voice policy specifies. Microsoft documents this as the supported way to bring third-party PSTN connectivity into Teams Phone (learn.microsoft.com).

In practice the call path looks like this:

• Teams client places the call and applies your voice routing policy.
• SBC (physical appliance or cloud-hosted) authenticates, secures and translates the call.
• SIP trunk carries the call to your carrier and out to the PSTN.
• Dial plans and least-cost routing decide which trunk and number range each call uses.

A SIP trunk is the carrier-grade line that replaces legacy ISDN; the SBC is what makes that trunk safe to expose to Teams.

What's included in AMVIA's Direct Routing service?

AMVIA delivers direct routing as a managed service: design, build, number porting, testing and ongoing support. UK-based engineers own the configuration so your internal team never touches SBC firmware or SIP signalling. Everything is scoped to your site count, call volumes and resilience needs before a single number moves.

Our four-stage rollout:

1. SBC and trunk setup — we provision SIP trunks and configure the SBC to connect your carrier to Teams. 2. Number porting — your existing numbers are ported to the new trunk; we manage the carrier process end-to-end. 3. Call routing and policies — voice routing policies, dial plans and emergency calling are configured for every call scenario. 4. Testing and go-live — internal, external and international call testing, then a phased rollout to your team.

This pairs naturally with Microsoft Teams Calling and a hosted phone system where you want handsets, call queues and auto-attendants alongside softphone calling.

Direct Routing vs Microsoft Calling Plans: which should you choose?

Direct routing gives you carrier choice and competitive call rates; Calling Plans give you a faster, Microsoft-billed setup with less flexibility. The right answer depends on whether you already have a carrier relationship, need geographic number ranges, or want least-cost routing across high call volumes.

Direct routing is the route most UK businesses pick when they want to keep an existing carrier.

Why do UK SMEs need Direct Routing now?

The UK's analogue phone network is closing. Openreach is migrating every line to digital, with switch-off completion scheduled for January 2027 (Openreach), which means legacy PBX and ISDN telephony has a hard end date. Moving Teams onto direct routing now removes that risk and consolidates voice into the platform staff already use.

The wider shift to digital landlines is documented by the regulator (ofcom.org.uk). Acting early gives you:

• A clean cut-over instead of a rushed, deadline-driven migration.
• One bill and one platform for calls, chat and meetings.
• Number continuity — your geographic numbers port across untouched.

For organisations with several offices, multi-site VoIP topologies let a single SBC route calls for every location, or local SBCs add resilience site by site. The PSTN switch-off guide covers the migration timeline in full.

Is Microsoft Teams Direct Routing secure?

Yes — when the SBC is hardened and the SIP trunk is correctly authenticated. The SBC is the security boundary between Teams and the PSTN, so it must enforce encryption, fraud controls and call admission limits. AMVIA configures these by default, because exposed voice infrastructure is a common toll-fraud target.

Security is the connective tissue across everything we run. Direct routing inherits the same controls we apply to VoIP security more broadly — encrypted signalling, monitored trunks and rate limiting. Microsoft sets out the platform-side controls for Teams telephony in its UK security guidance (microsoft.com/en-gb/security).

How much does Microsoft Teams Direct Routing cost?

Cost has three parts: Microsoft licensing (a Teams Phone-capable plan per user), SIP trunk and call charges from your carrier, and the SBC plus AMVIA's managed setup and support. Because trunk pricing and site count vary widely, we quote per environment rather than publish a single headline figure.

What shapes the quote:

• User count and licence type — every calling user needs a Teams Phone-capable licence.
• SBC model — on-premises appliance versus cloud-hosted, and whether you need redundancy.
• Number of sites and trunks — drives SBC topology and porting effort.
• Call profile — destinations and volumes determine the carrier tariff.

AMVIA holds Cyber Essentials Plus certification and Microsoft Solutions Partner status, and we manage IT and telephony for 1,200+ UK businesses — so the build is done once, correctly, by certified engineers. Critical issues are responded to within one hour.