PSTN Switch-Off | How to Migrate Your Business to VoIP

What is the PSTN switch-off and why does it matter?

The Public Switched Telephone Network is the copper infrastructure that has carried UK voice calls for over a century. Openreach is decommissioning it and replacing analogue lines with full-fibre and IP. When your exchange switches over, anything running on copper — voice, alarms, lift phones — stops.

Openreach set a final all-IP date of 31 January 2027 for the network (Openreach). Crucially, FTTC (Fibre to the Cabinet) broadband is itself a PSTN-dependent service: FTTC customers must migrate to FTTP or alternative IP-based connectivity before January 2027. The only forward path for voice is VoIP — telephony that sends calls as data rather than analogue signal.

Around 2.4 million UK businesses still operate on PSTN or ISDN lines, the majority being SMEs, with approximately 33% of large corporations still relying on analogue for some communications (2025 UK data). That is a lot of organisations leaving a hard deadline until the last minute.

What has already happened?

Stop Sell is live across most of the country, and ISDN30 has already ceased in the majority of exchange areas. The programme has been running since BT announced it in 2019, and the buying window for legacy lines has effectively closed.

• ISDN30 lines have been ceased in the majority of UK exchange areas
• New PSTN and ISDN orders are no longer accepted in most areas
• Openreach has completed FTTP deployment across a growing proportion of UK premises
• "Stop Sell" has been applied to legacy services wherever FTTP is available

If you cannot buy a new copper line today, that is the clearest signal that planning your migration to VoIP cannot wait. The UK full-fibre rollout is tracked under Project Gigabit.

How should a business plan the migration to VoIP?

A controlled migration follows six steps, in order: audit dependencies, check connectivity, choose a provider, plan number porting, decide endpoints, and resolve secondary lines. Rushing any step — especially the dependency audit — is where most post-migration outages come from.

Step 1 — Which lines and devices depend on PSTN?

Before you migrate anything, establish exactly what is connected. The non-voice dependencies are the most commonly overlooked part of PSTN planning and the most frequent source of post-migration problems.

• PSTN and ISDN lines — how many, which numbers, which sites
• Alarm lines — intruder and fire alarms often sit on separate PSTN lines
• Lift emergency phones — a regulatory requirement, usually on dedicated lines
• Fax machines — still used in some sectors; replaceable with internet fax
• Payment terminals — older card terminals may use PSTN; check with your provider
• CCTV dial-out lines — older systems use PSTN for remote monitoring

Step 2 — Is your internet ready for VoIP?

VoIP calls run over your internet connection, so connectivity quality directly sets call quality. Each VoIP call uses roughly 80–100 kbps with standard codecs, so ten concurrent calls need roughly 1 Mbps dedicated to voice. Capacity is rarely the problem — consistency is.

Assess current speed and type (FTTC, FTTP, leased line), contention during business hours, and — more important than raw speed — latency and jitter. If voice quality matters to revenue, a dedicated business leased line removes contention entirely, while solid business broadband suits smaller call volumes.

Step 3 — Which VoIP provider and platform?

The switch-off is a genuine prompt to test the market rather than defaulting to whatever your existing carrier proposes. Independent platforms such as Gamma Horizon, 3CX and Microsoft Teams Phone typically offer stronger features at lower cost than incumbent carrier VoIP. Compare on feature fit, uptime SLA, support quality, full-term pricing and included migration support.

A hosted phone system suits most SMEs; multi-site organisations with on-premise PBX kit may prefer SIP trunks. Whichever you pick, treat call security as part of the decision — see VoIP security for the controls that matter.

Step 4 — Can you keep your numbers?

Yes. Number porting transfers your existing 01, 02, 03 and 0800 numbers to the new provider. The process takes approximately 5–10 working days per batch. Build the new system, test it, then port — never the other way round.

• Complete and test the new VoIP system before porting
• Schedule porting for a low-traffic window (e.g. Friday end of day)
• Confirm porting has completed before decommissioning old lines

Step 5 — Which endpoints should you choose?

Traditional PSTN handsets do not work on VoIP, so every user needs a new endpoint. Most businesses mix desk phones for fixed roles with softphones and mobile apps for everyone else.

Step 6 — How do you handle alarms, lifts and fax?

For every secondary line found in Step 1, confirm a migration path before the exchange switches. These are the dependencies that cause genuine safety and compliance issues if missed.

• Alarm and CCTV: ask the monitoring company for a VoIP-compatible or 4G/IP dialler
• Lift phones: ask the lift manufacturer for an IP-compatible emergency phone
• Fax: replace with an internet fax service, or retire if no longer used
• Payment terminals: ask your payment provider for a modern IP-based terminal

What happens if you do nothing?

If you take no action, Openreach and your carrier will migrate you when your exchange switches — on their terms, to their products, on their timing. You lose the chance to compare providers, negotiate contract length, and test before cutover. Proactive migration keeps all three decisions in your hands.

AMVIA manages the complete PSTN migration for UK businesses end to end — one accountable provider handling all six steps so there is no disruption to your communications during the move. One provider. Security-first. Microsoft-certified.