PSTN and ISDN switch-off 2027: what your business must do

What is the PSTN and ISDN switch-off?

The PSTN (Public Switched Telephone Network) is the traditional copper landline network that has carried UK calls for decades. ISDN is the digital service many businesses use for multiple lines and switchboards. Openreach is retiring both, and the national switch-off date is 31 January 2027.

This is not a request or a recommendation. Once the network closes, calls no longer route over it, and lines that still depend on it simply go dead. Sales of new PSTN and ISDN lines have already stopped across most of the country, and some exchanges are switching off ahead of the national date as part of the phased programme.

The replacement is voice over IP, where calls travel as data over your broadband instead of a dedicated copper line. If you are new to this, our guide on what VoIP is and how it works covers the basics. The practical message for businesses is simple: you need a plan to move every phone and every connected device off the old network before the deadline.

What is affected besides my phones?

The switch-off catches more than handsets. Anything plugged into a phone socket that relies on the PSTN or ISDN will be affected. This is the part businesses most often forget, because these devices have sat quietly working for years.

Check for all of the following:

Device or service	Why it matters
Monitored alarms	Many send signals to a monitoring centre over the phone line. They need an IP or mobile signalling path before 2027.
Lift emergency phones	The autodialler in a lift often uses a PSTN line. A failed line is a safety and compliance issue.
Door entry systems	Intercoms and gate controllers that dial out over a line need replacing or re-routing.
Card machines (PDQ)	Older terminals dial out to authorise payments. Most newer machines use broadband or mobile data already.
CCTV and remote monitoring	Some legacy CCTV uploads over a phone line. Move to IP-based connectivity.
Fax and franking machines	Both can run over the old line. Replace with email-to-fax or IP equivalents where still needed.

The safe approach is to treat the switch-off as a full audit of everything connected to a line, not just a phone upgrade. Speak to each device supplier early, because lead times for alarm and lift upgrades can be long.

How do I prepare? A step-by-step checklist

Preparing is straightforward if you work through it in order. Follow these steps and you will be ready well before the deadline, with no scramble in January 2027.

1. Audit every line and connected device. List all your phone lines, ISDN channels, broadband types and anything plugged into a phone socket: alarms, lifts, door entry, card machines, CCTV and fax. Note which run over the old PSTN or ISDN network.
2. Check your broadband. Confirm you have a suitable internet connection for VoIP, such as FTTP or SoGEA. Each call needs about 100 kbps each way, so most business broadband is fine. Order an upgrade if you are still on a copper-only line.
3. Choose a hosted VoIP provider. Pick a UK hosted VoIP or cloud phone provider that includes UK numbers, number porting, mobile and desktop apps, call routing and the call handling features you use today.
4. Port your existing numbers. Ask your new provider to port your current business numbers across. You keep the same numbers, and the new provider manages the move so you do not lose them.
5. Sort out connected devices. Replace or re-route anything that relied on the old line. Move alarms, lifts and card machines to IP-based or mobile alternatives, and check with each device supplier well before the deadline.
6. Test in parallel, then go live. Set up the VoIP system alongside your old lines, test calls in and out, confirm routing and voicemail, then go live and cancel the old PSTN or ISDN lines once everything works.

For a deeper walkthrough of the move itself, see our guide on how to switch your business phones to VoIP.

Can I keep my business numbers?

Yes. Keeping your numbers is one of the most common worries, and the answer is reassuring: porting your existing numbers to a VoIP provider is a normal, usually free part of switching. You do not cancel your old line first and then hope a new number is acceptable to customers. The new provider arranges the port, and your numbers carry across.

Geographic numbers (01 and 02), 03 numbers such as 0333 and 0345, and 0800 freephone numbers can all be ported. Timescales vary by number type and your losing provider, ranging from a few working days for a single number to around two weeks for larger or non-geographic ranges. Our full guide on keeping your number when switching to VoIP explains the process and how to avoid any downtime during the move.

Because porting is scheduled, you can line up the switch so callers never notice. The old line and the new VoIP service run side by side until the port completes, then the old line is retired.

Why switch early rather than wait until 2027?

The deadline is fixed, but the work to get ready is not instant. Replacing a monitored alarm, upgrading a lift autodialler or ordering a full-fibre install can each take weeks, and demand will spike as the date approaches. Leaving it late risks installers and provider porting teams being booked up exactly when you need them.

Switching early also brings benefits you can use now. A hosted VoIP system gives you features the old network never could: an auto-attendant that answers and routes calls, ring groups and call queues, voicemail-to-email, call recording, and apps so staff can take calls on a mobile, a browser or a desk phone. Some systems, including Voxora, add an AI Receptionist that answers calls 24/7, handles common questions and transfers to the right person.

In short, the switch-off forces a change, but it is a change worth making sooner. You remove a future risk, you spread the work over a comfortable timescale, and your team gets a better phone system in the process.