PSTN & ISDN switch-off: what, why, when, and how to future-proof your business

What is the PSTN switch-off? #

The PSTN is the copper wire network that’s carried voice calls for over a hundred years. It also supports ISDN lines, which many businesses still use for PBX systems and other legacy infrastructure. But this analogue system was built for a different era, and it's being retired.

Since 5 September 2023, no new PSTN or ISDN services can be ordered in the UK. Openreach has locked them behind a nationwide "stop-sell", and by 31 January 2027, all remaining lines will be permanently disconnected.

The PSTN is the copper wire network that’s carried voice calls for over a hundred years. It also supports ISDN lines, which many businesses still use for PBX systems and other legacy infrastructure. But this analogue system was built for a different era, and it's being retired.

Since 5 September 2023, no new PSTN or ISDN services can be ordered in the UK. Openreach has locked them behind a nationwide "stop-sell", and by 31 January 2027, all remaining lines will be permanently disconnected.

Why is it happening? #

There are several good reasons why the PSTN is being switched off, and none of them are optional.

First, the infrastructure is ageing. Replacement parts are scarce, outages are becoming more frequent, and maintenance costs have risen sharply, a burden that ultimately feeds through to higher line rental. Government guidance notes that the network is increasingly unreliable and costly, prompting communication providers to agree a firm retirement date.

Second, the UK has made huge progress in rolling out full-fibre broadband. Openreach alone now passes more than eighteen million homes and business premises with full-fibre broadband and continues to add about a million more every few months (as of the time of this writing). This digital backbone supports modern VoIP (Voice over IP) services, which are cheaper, greener and more flexible than copper-based systems.

Finally, all-IP communications unlock features that legacy systems simply can’t offer: smart call routing, remote access, advanced analytics, integration with Teams or CRM systems, and seamless support for hybrid working.

The switch-off is about more than replacing phones. The PSTN switch-off therefore offers businesses not just a problem to solve but a platform for productivity gains. It’s about enabling smarter, scalable communications for the future.

When is it happening? #

Here are the key deadlines:

• September 2023: Openreach began the stop-sell of new PSTN/ISDN services.
• By end December 2025: Businesses encouraged to complete migration to IP solutions.
• 31 January 2027: Final switch-off deadline after which PSTN/ISDN services will cease nationwide.

All major telecom providers including BT (including EE), Vodafone, O₂ (via Virgin Media O₂), Sky, Plusnet, are aligned to this timetable

Across the industry, the message is clear: don’t wait until 2026. Network engineers, service desks and equipment suppliers are already seeing increased demand. The earlier you plan your move, the smoother the process will be.

What’s at risk if you wait? #

The most obvious risk is downtime. When the network shuts off, any PSTN-connected device that hasn’t been migrated will simply stop working.

That could include:

• On-site private branch exchange systems still using ISDN lines
• Alarm panels that dial out over copper
• Payment terminals (PDQ/EPOS)
• Fax or telemetry lines

You might not even know how many of these services are hiding in your estate. In many businesses, they're scattered across multiple sites and have been “just working” for years. But if they’re still running on PSTN, they won’t survive past 2027.

You’re also at risk of rising costs. Installs for FTTP and SoGEA are becoming more expensive and as more users leave the PSTN, the price of maintaining legacy infrastructure climbs. Delaying migration means spending more for a service that’s getting worse.

And then there’s lost opportunity. VoIP and cloud telephony offer real benefits: geographic flexibility, easier scaling, better user experience and more insight into how your teams communicate.

Four steps to future-proof your communications #

You don’t need to overhaul everything at once. But you do need a clear plan. Here’s how to start:

1. Audit Your Connectivity Lines
   Map every phone number and connected device across your estate. Be thorough and include often-overlooked equipment such as lift intercoms, alarm systems, card payment terminals, and fax lines hidden in storerooms or remote offices.
2. Check Your Current Setup
   Make sure your broadband or fibre connection can reliably support voice traffic, especially during peak usage. For critical services, consider adding mobile back-up or an uninterruptible power supply (UPS) to maintain communication during outages.
3. Choose Your Internet Protocol Solution
   Decide on the best-fit replacement for your current system, this might be a cloud-hosted phone platform, SIP trunks that retain your existing phone system, or Microsoft Enterprise solutions integration for a unified communications approach. Consider scalability, remote working support, and compatibility with existing tools.
4. Plan the Switchover
   Approach the transition in structured phases. Start with low-risk locations, allow time for staff training, and build in contingency testing to ensure a smooth, disruption-free migration before the 2027 deadline.

Don’t wait for the deadline #

The countdown is on. The stop-sell has already passed. The 2027 switch-off isn’t a vague future risk, it’s a fixed date on the calendar.

If you want to avoid service interruptions, rising costs and missed opportunities, now is the time to act.

Let’s talk. Book a call with Revolve Communications and we’ll help you build a PSTN exit plan that’s fast, future-proof and fully aligned to your business needs.