The UK PSTN and ISDN phone networks are switching off on 31 January 2027. Stop-sell is already live — no new traditional lines can be ordered. If your business still has analogue lines or ISDN30, move to VoIP (Microsoft Teams Phone, 3CX hosted, or a Gamma-backed cloud platform) during 2026. Don't leave it to Q4. Around 500,000 UK business lines were still on legacy in February 2026.
What's actually happening
BT is retiring the Public Switched Telephone Network (PSTN) and Integrated Services Digital Network (ISDN). The target date has slipped once — originally December 2025 — but 31 January 2027 is the current firm date across almost every UK exchange. From that date, traditional copper-carried voice services stop working. All calls move to internet-based technology.
"Stop-sell" has been in force since mid-2023 in most exchange areas. You can't order new PSTN or ISDN lines; you can only keep what you have until the final switch-off. Openreach's own milestone reporting confirms the 2027 target date and the exchange-by-exchange migration programme.
What's replacing it
Voice over IP (VoIP). Calls travel as data packets over your internet connection rather than a dedicated copper pair. For small-business users, the main 2026 options are:
- Microsoft Teams Phone — integrates with Microsoft 365, great if your team already lives in Teams. Licence from around £6 per user per month plus calling plan.
- 3CX hosted — self-contained PBX in the cloud, flexible handsets, often cheapest per user at scale.
- Cloud PBX on Gamma, Wildix or TelcoSwitch — traditional-feel hunt groups, receptionist console, call recording.
Our business telephony page lays out which is right for which use case. For most SMEs we lean Teams Phone for hybrid teams and 3CX for call-heavy offices.
Why this matters now, not in Q4
Three reasons to move in 2026 rather than waiting:
- Provider capacity. The UK industry is migrating hundreds of thousands of business lines in the run-up. Install slots in Q4 2026 will be scarce. Book now for autumn.
- Number porting takes weeks. Geographic numbers typically port in 10–15 working days. Complex multi-number orders can slip to 4–6 weeks.
- Dependent kit. Alarms, lift emergency lines, door entry, PDQ credit-card terminals, fax machines and some franking machines use analogue lines. Audit everything before you cut over.
A sensible 12-week plan
This is how a typical 15–30 user West Sussex business moves off PSTN cleanly:
- Week 1–2 — Audit. Every active line, what it does, who calls it, where it terminates. Bills, router logs and wall sockets all help.
- Week 3–4 — Shortlist. Pick VoIP platform, calling plan, number ranges to port. Confirm broadband is strong enough (symmetric FTTP preferred; a backup connection or SoGEA matters).
- Week 5–6 — Order and configure. New handsets, Teams calling licences, ring groups, voicemail, out-of-hours flows.
- Week 7–8 — Parallel running. Route new calls to VoIP while PSTN still accepts inbound. Iron out dial plans and call-recording.
- Week 9 — Port numbers. Submit Letter of Authority to the new provider; they coordinate with the losing carrier. Numbers flip on the agreed date.
- Week 10–12 — Cease old lines, train staff, document.
The awkward bits: alarms, lifts and old kit
Not everything translates to VoIP. Common casualties:
- Monitored intruder alarms — many use an analogue dialler to reach the Alarm Receiving Centre. Replace with an IP or 4G signalling path (Dualcom, Emizon).
- Lift emergency phones — legally required 24/7 two-way voice. Fit a cellular unit or an approved IP dialler.
- Card machines — legacy PDQ units often use analogue. Most acquirers ship IP or 4G replacements for free.
- Door entry and gate systems — move to GSM units.
- Fax machines — move to email-to-fax or an internet-fax service.
Get this list right early. It's where we see avoidable weekend callouts.
Costs to expect
Per user in a typical SME cloud-voice deployment:
- Platform licence (Teams Phone or 3CX seat): £4–£10 per user per month
- Calling plan (UK landline + mobile inclusive): £4–£8 per user per month
- Handset (if needed): £80–£180 one-off
- Number porting: £10–£25 per number
- Setup and configuration: £250–£1,500 depending on complexity
Most businesses end up paying a similar monthly total to their old line-rental-plus-minutes, but gain hunt groups, call recording, softphone apps, and the ability to work from anywhere.
Common mistakes
- Leaving it until Q4 2026 — installers will be full.
- Assuming current broadband is good enough (check upload speed, jitter and QoS).
- Forgetting the alarm or lift line until install day.
- Signing a 60-month cloud contract when the 2027 rush is already here; 36 months is plenty.
- Buying handsets from one vendor then realising they're locked to another PBX.
FAQs
When is the PSTN switch-off?
The UK PSTN and ISDN networks are scheduled to be switched off on 31 January 2027. Stop-sell is already in place across most exchanges — you can't order new traditional lines, only keep existing ones until the final date.
What replaces PSTN?
Voice over IP (VoIP). In small-business practice, that's Microsoft Teams Phone, 3CX hosted, or a cloud platform from a provider like Gamma or Wildix.
Will I keep my number?
Usually yes. Geographic numbers (01403, 01293, 01903, 01243) can be ported to most VoIP providers. Port timing is typically 10–15 working days from the signed Letter of Authority.
What about alarm and lift lines?
These need specialist handling. Some analogue devices won't work over VoIP and need IP-based replacements or a cellular fallback — particularly intruder alarms, lift emergency phones and some card terminals.
Can I wait and see?
Not really. Around 500,000 UK business lines were still on legacy in early 2026 and every one needs migrating before the January 2027 date. Install capacity in Q4 2026 will be the tightest it has ever been.