VoIP and Microsoft 365: Integrating Calling with Teams

What does it mean to run VoIP through Microsoft 365?

It means your phone system stops being a separate platform and becomes a feature of Microsoft 365. Microsoft Teams already handles internal calls, video meetings and chat; Teams Phone bolts on a calling layer to the public telephone network, so the same app dials any UK or international number.

Every Microsoft 365 Business plan includes Teams, which is the most widely deployed collaboration platform in the world — over 320 million monthly active users globally (Microsoft, 2024). Teams Phone uses that existing footprint rather than asking staff to learn a second tool. There is no extra phone app, and no new hardware beyond the PCs, laptops and smartphones people already carry. This is the natural next step once you have adopted business VoIP solutions and want one accountable platform instead of two.

• Dial and receive on any business number directly inside Teams
• One set of credentials, one mobile app, one support contract
• Voicemail, transfers, queues and call recording in the same interface

How does Microsoft 365 connect to the phone network?

Teams handles Teams-to-Teams calls over Microsoft's cloud natively. To reach external numbers it must connect to the public telephone network, and there are three ways to do that. The right one depends on your call volumes, number estate and how much infrastructure you want to manage.

For most UK SMEs, Microsoft Teams Direct Routing wins on cost and number flexibility. Your existing numbers are ported to a SIP trunk provider and calls route through Teams via an Azure-certified Session Border Controller — the bridge that handles call setup, security and media conversion. AMVIA owns the SBC and carrier relationship as a fully managed service. Microsoft documents all three models in its Teams Phone deployment guidance.

What Microsoft 365 licence do you need for Teams Phone?

Teams Phone needs a Teams Phone Standard licence added to a Microsoft 365 plan that already includes Teams. The add-on typically costs around £7–10 per user per month (market rates as of 2026) and is only required for users who make external calls. People who only need internal Teams calls, meetings and chat do not need it.

The add-on is included as standard in Microsoft 365 E5, but must be purchased separately on Business Basic, Business Standard, Business Premium, E1 and E3. Microsoft publishes its UK plan list prices — Business Basic £4.60, Business Standard £9.60 and Business Premium £16.90 per user per month (ex VAT, annual) — on the Microsoft 365 UK pricing pages. Even with the Phone System add-on, the combined cost is usually lower than running a standalone phone system alongside Microsoft 365. AMVIA reviews your licence estate and recommends the cheapest compliant configuration.

Why do UK SMEs need this now?

The UK PSTN is being switched off, and businesses still on ISDN have to move to a digital service before it goes. Doing that move through Microsoft 365 lets you retire the old lines and the old phone system in a single transition, instead of swapping one piece of legacy kit for another.

The switch-off completes by 31 January 2027 (Openreach), and around 2.8 million lines still remain on the PSTN — more than 500,000 of them serving business premises (Openreach, 2026). You can read the regulator's own position on the migration on the Ofcom PSTN switch-off pages. For a business already living in Outlook, Teams, SharePoint and OneDrive, Teams Phone is usually the most cost-effective path off ISDN. AMVIA covers the deadline in detail on the PSTN switch-off guide.

• Voicemail lands in your Teams and Outlook inbox, transcribed and searchable
• Call history sits alongside chat history for each contact
• Presence shows colleagues your availability before they call

What features come with Teams Phone?

Once Teams Phone is live with PSTN connectivity, UK businesses get a full enterprise calling feature set inside Teams. There is no separate handset platform to administer — everything is configured through the Teams admin centre and managed by AMVIA.

• Inbound and outbound calling to any UK, mobile or international number on PC, Mac, iOS or Android
• Auto-attendant greetings and menus that route callers to the right department
• Call queues distributing calls by simultaneous ring, round-robin or longest idle
• Voicemail with transcription delivered to Teams and Outlook
• Call transfer, hold, park and conferencing, with one-click escalation to video
• Call recording for compliance, training or quality assurance, stored in Microsoft's cloud
• Desk phone support for Teams-certified IP handsets from Yealink, Poly, and AudioCodes

Each concurrent call uses roughly 80–100 Kbps, so a stable, low-latency connection matters; Microsoft sets out the network requirements for Teams in its admin documentation. AMVIA assesses your connectivity before migration to confirm it supports peak call volumes.

What should you plan before migrating?

Treat the move as a project, not a switch flip. The technology is proven, but a clean cutover depends on getting licensing, numbers, call flow and connectivity lined up first. AMVIA runs this checklist on every Teams Phone deployment.

• Verify the licence tier so every external caller has a Teams Phone Standard add-on
• Choose the connectivity method — Direct Routing or Operator Connect usually beat Calling Plans on UK value
• Plan number porting — moving geographic numbers to a Teams-compatible carrier takes 7 to 14 working days
• Assess the internet connection for bandwidth and latency under peak load
• Map existing call flow — auto-attendants, hunt groups, DDIs and voicemail — so Teams replicates it correctly
• Configure 999 access with location information for every Teams Phone user

Calling is also a security surface. Migrating telephony into Microsoft 365 means it inherits your identity and conditional-access controls, which is why we align it with VoIP security and your wider Microsoft 365 security posture rather than treating the phone system as a standalone box.