The ISDN and PSTN switch-off: what actually happens in January 2027

The UK's old telephone network is being turned off on 31 January 2027. Not upgraded, not phased down. Turned off.

Every analogue phone line, every ISDN circuit and every broadband service that runs over them stops working on 31 January 2027. The deadline has already been pushed back once, from December 2025, and Openreach has been clear that it will not move again.

If your business still has traditional lines, you have months to sort this, not years. Around 2.8 million lines were still on the old network at the start of 2026, more than half a million of them serving business premises. That is a lot of migrations trying to squeeze through the same door at the same time, which is exactly why we'd suggest not leaving it until the autumn of 2026.

What is actually being switched off?

The PSTN, the Public Switched Telephone Network, is the copper network that has carried UK phone calls for over a century. When it goes, so does everything built on top of it:

Analogue phone lines. The standard business or home landline.

ISDN2 and ISDN30. The digital lines that most office phone systems ran on for decades. If your phone system is more than about ten years old, there is a fair chance it uses ISDN.

Old broadband. ADSL and standard FTTC broadband both run over the same copper. These are being withdrawn too.

The quiet dependencies. This is the part that catches people out. Fire and intruder alarms, lift emergency phones, door entry systems, card payment terminals and franking machines are often wired into an analogue line that nobody has thought about since it was installed. When the line dies, so do they, and an alarm line failing is not something you want to discover after the fact.

Why is it happening?

The honest answer is that the copper network is worn out. Openreach reported a 20 percent rise in PSTN faults in a single year, spare parts are getting hard to source, and the engineers who know the old kit are retiring. At this point the old network is a bigger reliability risk than the new one. The replacement for everything is IP: calls travel over an internet connection instead of dedicated copper.

There is a financial push too. Line rental on legacy products is rising in steps through 2026, roughly doubling by October. Staying put is not the cheap option it looks like.

How to check if you're affected

Three quick tests:

1. Look at your phone bill. If it mentions line rental, ISDN, WLR or an analogue line, you're affected.
2. Ask whoever looks after your phone system how it connects. If the answer involves ISDN, you're affected.
3. Walk the building. Find the alarm panel, the lift phone, the card machine, the door entry system. Anything plugged into a phone socket needs a plan.

If you're a Netcalibre customer in a calibrated building, you can skip this bit. Your services are already all-IP and nothing changes for you in January 2027.

What replaces it

Phone lines become VoIP, calls over the internet. Done properly it is better in every way that matters: your numbers move with you, calls ring on desk phones and mobiles at once, and you get call recording, menus and reporting that ISDN never offered. Your existing numbers port across, so nothing changes for the people calling you.

The one thing VoIP is only ever as good as is the connection underneath it. Calls over a congested shared broadband line sound like calls over a congested shared broadband line. That is why we run voice over dedicated fibre, where your bandwidth is yours alone and call quality doesn't depend on what the office next door is downloading.

The alarm lines, lift phones and payment terminals each have IP-based replacements as well. Your alarm company and lift maintainer will have heard this question many times by now; the important thing is to ask it before 2027 rather than after.

A sensible timeline from here

Between now and autumn 2026: audit what you have, including the forgotten lines. Choose your replacement and get the order in. Installations and number porting both have lead times, and both will stretch as the deadline gets close and the queue grows.

Well before January 2027: run the new system alongside the old for a period. Port the numbers when you are confident. Then cancel the legacy lines and stop paying rising rent on a dying network.

If you do nothing, your provider may shunt your line onto a basic emergency-only fallback, which keeps 999 working and not much else. It is not a plan, it is a parachute.

The short version

The switch-off is real, the date is final, and the businesses that move early get a calm migration at a sensible price. The ones that wait get whatever engineering slots are left in January 2027.

If you'd like a hand working out what you're running and what it should become, call us on 020 3026 2626 or use the button below. If your building is one of ours, the hard part is already done.

Not sure what you're running?

Tell us what's on the bill and we'll tell you what it should become.