The PSTN switch-off: what 31 January 2027 means for your business

The PSTN switch-off is the closure of the UK's old analogue phone network, and BT Group has confirmed it will retire the network by 31 January 2027, with ISDN lines going at the same time. Any business still using a traditional phone line, or equipment that connects through one, needs to move to a digital service before then. For most small businesses the change itself is straightforward and takes about a week. What tends to get missed is rarely the phones on desks but the alarm, card machine or lift that has used the same line for years without anyone thinking about it.

What is the PSTN switch-off?

The PSTN, or public switched telephone network, is the copper network that has carried UK landline calls for decades. ISDN is the digital service many businesses used for multiple lines and office phone systems, and it depends on the same network, so the ISDN switch-off happens on the same date. Both are being replaced by phone services that run over an internet connection, usually called VoIP. BT Business says that services which haven't been moved, including ISDN, will stop working from 31 January 2027.

The deadline doesn't depend on where you are. Earlier stages of the upgrade were rolled out area by area, which is why so many people search for switch-off dates in their postcode, but 31 January 2027 is the end date everywhere. The government's guidance on moving landlines to digital technologies asks businesses to check their equipment, speak to their provider and move at the earliest opportunity rather than waiting to be contacted.

What happens if your business hasn't switched by 31 January 2027?

Lines that haven't moved won't all go dead overnight, but they won't carry on as they do now either. Openreach has confirmed that lines still on the old network after the deadline will be moved onto a temporary emergency voice service, which it describes as limited and more expensive than modern alternatives, as reported by ISPreview in September 2026. Phone providers will pay Openreach £35 a month for each of those lines from 1 February 2027, before adding their own charges.

At the same point, Openreach said about 1.2 million lines still hadn't moved, including around 350,000 at business premises. With that many lines left and a fixed date, engineers and number transfer teams are likely to be at their busiest in the final weeks, which is the main reason not to leave it until January.

Which business equipment uses a phone line?

The phones are the obvious part, but Openreach and BT also list intruder and fire alarms, lift emergency phones, card payment terminals, door entry systems, CCTV and fax machines among the equipment that can depend on the old network, and Openreach counted more than 12,000 lift lines alone that still needed to move.

Some of this equipment will keep working on a digital line, some needs an adapter or a settings change, and some needs replacing. Alarms and lifts matter most, because they're usually only tested when something goes wrong, so ask the company that maintains them whether they signal over a phone line and what they need after the switch. Your payment provider can tell you whether your card machines connect over broadband, mobile data or a phone line. Openreach will also test business equipment in its own labs to check whether it works on a digital line.

Broadband can be affected too. Older ADSL broadband runs over the same copper and BT Business says it's being withdrawn by the same date, so if your internet comes bundled with a traditional phone line, check with your provider which type you have before you change anything else. If nobody in your business looks after IT day to day, this is the kind of check an IT support team that already knows your setup can do for you, alongside the list of lines and devices above.

What should you replace your phone lines with?

For most businesses of 5 to 200 people, the replacement is a cloud phone system. Your numbers move to a service that runs over your internet connection, and your team answers calls on desk phones, a computer or a mobile app. You keep your existing numbers and gain things a traditional line never offered, such as calls that follow people when they work from home, ring groups so a call reaches whoever is available, and different routing for evenings and bank holidays.

The question businesses usually ask is what happens if the internet goes down. A cloud phone system can divert calls to mobiles automatically, so customers still get through, which is often better than an old office line that simply rang out when nobody was at a desk. It's worth deciding that routing when you set the system up rather than after the first outage.

How long does switching take?

Moving to a cloud phone system normally takes about a week, and most of that is waiting for your numbers to transfer from your current provider. The work runs in four stages: listing your numbers and who answers each one, setting up and testing the new system, transferring the numbers, and going live. Your existing lines keep working until the numbers move, so calls aren't lost in between. Check your current phone contract before you give notice, because some carry an exit charge and the number transfer depends on your current supplier's terms.

Is your business ready for the switch-off?

These questions cover the gaps that most often leave a business caught out.

• Do you know which of your numbers are still on a traditional line or ISDN?

• Has your alarm company confirmed your alarm will keep signalling after the switch?

• Do you know how your card machines connect?

• Does your broadband depend on a traditional phone line?

• Do you know who your phone contract is with and when it ends?

Any "not sure" is worth checking this month, while there's still time to move without a rush.

The short version

The UK's analogue phone network closes on 31 January 2027, and ISDN closes with it. Find every number and every device that uses a traditional line, ask your alarm, lift and payment providers what they need, and move your numbers to a cloud phone system well before the deadline, when engineers and transfer teams will be at their busiest.

Our business phone systems page explains how we move your numbers onto a cloud phone system, from £22 per extension a month with 5,000 UK minutes included and a one-off £36 for number porting, usually within about a week and with no contract.