3CX vs Microsoft Teams Phone — the hidden-cost honest comparison.

What you're actually buying with Teams Phone.

Microsoft Teams Phone is not one product. It's a stack of licences that work together. To make and receive real PSTN calls from a UK Teams client, you need three things:

1. An M365 licence with Teams included. Business Basic (£5.10/user) doesn't include the Teams admin features required. Business Standard (£10.20/user) or higher is the floor for most SME deployments. Already paying this — fine.
2. Teams Phone Standard licence. Microsoft's add-on at £6.30 per user per month. Gives you the dial pad, voicemail, and basic call routing in the Teams client. Does not give you actual PSTN calling.
3. A calling plan, or a Direct Routing setup. Microsoft Calling Plan UK Domestic adds £10.20 per user per month plus VAT and includes call minutes. Alternative: keep Teams Phone Standard and use Direct Routing through a third-party SIP provider (e.g. via 3CX, Gamma, or Operator Connect).

Stacked all-in, the real Teams Phone Microsoft-only cost lands at £21–26 per user per month for an M365 Business Standard customer adding Teams Phone Standard + Calling Plan. Most UK procurement teams realise this on month two of using it, when the first invoice arrives looking 3× the £6.30 figure they remembered from the conversation with their account manager.

3CX with Teams direct routing — what that actually means.

3CX AI tier (16+ SC) provides Microsoft Teams Direct Routing. Users dial out from the Teams client exactly as before; PSTN calls route through 3CX, which connects to UK SIP trunks (typically Gamma). The Teams user experience is unchanged; the call-routing infrastructure underneath is 3CX instead of Microsoft Calling Plan.

The cost stack for this configuration:

• 3CX AI licence: from £480/yr at 8 SC (up to 40 users), £910/yr at 16 SC (up to 80 users). Per-system, not per-user.
• 3CX hosting: partner-managed UK hosting ~£25–60/month depending on SC band, or 3CX-hosted at £245/yr for 8–16 SC.
• UK SIP trunks (Gamma): ~£3–4 per channel per month wholesale, marked up modestly by partner.
• Existing M365 / Teams Phone Standard licences: you still need M365 Business Standard or higher. You do NOT need Teams Phone Standard — that's replaced by 3CX. You do NOT need a Microsoft Calling Plan — that's replaced by 3CX direct routing.

All-in this lands at roughly £6–10 per user per month for the 3CX layer, on top of your existing M365 subscription. The M365 cost is the same either way; you're replacing the Teams Phone Standard + Calling Plan stack (£16.50/user) with 3CX-managed direct routing (£6–10/user).

Pricing at 50 users.

Microsoft Teams Phone pricing snapshot May 2026 (microsoft.com/en-gb/microsoft-teams/business-voice). Ex-VAT. 3CX numbers from our cost stack — see honest pricing for the decomposition.

Where Teams Phone wins.

• Single-vendor procurement. Your existing Microsoft EA / CSP relationship covers it. No new vendor, no new contract, no new supplier evaluation. Worth real procurement points.
• You're fully committed to Microsoft for everything. If you run Defender for everything, use SharePoint for everything, and have built the firm's identity layer entirely on Azure AD, Teams Phone keeps the consolidation tight.
• You only need basic call routing. If the firm's telephony need is "dial out, receive inbound, transfer to a colleague" — and you don't need advanced queues, call recording with retention controls, IVR with multi-level branching, or hot desking — Teams Phone covers it.

Where 3CX with Teams direct routing wins.

• Real PBX features Teams Phone doesn't include. Advanced call queues with announced wait time, skills-based routing, configurable recording with retention policy, IVR designer, hot desking, switchboard, reception overflow logic. Teams Phone has basic versions of some of these; 3CX has the full feature set.
• UK data residency on recordings. Teams Phone call recordings sit on Microsoft's chosen Azure regions (often EU). 3CX-managed through a UK partner hosts recordings on UK soil — cleaner audit trail for regulated sectors.
• Per-system pricing. Adding 10 users to Teams Phone costs £160+/month forever. Adding 10 users to 3CX costs handsets and admin time — no ongoing per-user cost.
• Same Teams user experience. Critical: Direct Routing means users still dial from the Teams app, see contacts in Teams, get call notifications in Teams. Nothing visibly changes. The infrastructure underneath changes.
• Honest 24-month TCO. The £10k saving over 24 months at 50 users is real money — staff bonus, marketing budget, or a senior hire.

Who should pick which.

• Pick Teams Phone if: you're under 25 users, your phone needs are basic, you're a Microsoft-everything procurement culture, or the simplicity premium of single-vendor outweighs the cost differential.
• Pick 3CX with Teams direct routing if: you're 25–250 users, you need real PBX features (queues, recording, IVR), you care about TCO, or you want UK data residency without sacrificing the Teams UX.

What we'll tell you at audit.

The Teams Phone-vs-3CX question is the most-common UK SME audit conversation we have. The honest answer depends on how you actually use the phones — if the answer is "Teams chat with the occasional PSTN call", Teams Phone may genuinely be fine. If the answer involves "reception", "queues", "recording", or "we need 50 people to dial outbound efficiently", 3CX-managed with direct routing wins on cost and feature breadth. Book a free audit and we'll model both against your actual situation.