31 January 2027 is the deadline for the retirement of BT’s traditional phone network. If your business still relies on ISDN or analogue phone lines, it’s time to plan how those services will move to digital alternatives.

For many businesses, the first thought will be their telephone system. But the switch-off could affect more than the phones on your desks. An older line may also connect a card machine, alarm, door entry system or lift phone. Finding those connections is one of the most important parts of preparing for the change.

The good news? You still have time to get organised. Here’s what the switch-off means and where to start.

What is actually being switched off?

The Public Switched Telephone Network, or PSTN, is the traditional network used to deliver analogue phone services. ISDN, which many businesses have used for years to make and receive calls, also depends on older network technology.

BT plans to retire its PSTN by 31 January 2027. Businesses using services that rely on it will need to move to a suitable digital alternative before their old service ends.

You may hear this referred to as the ISDN switch-off, the PSTN switch-off or the move to digital phone lines. The names can make it sound more complicated than it is. In simple terms, the technology behind traditional phone services is changing, and businesses need to check that their calls and any connected equipment will continue to work.

Does this affect every business?

Not necessarily in the same way. You might already be using a digital phone system for your main business number, but still have an analogue line elsewhere in the building. Equally, a business with several premises may have updated one site and overlooked another.

If you’re unsure what type of service you have, that’s a sensible place to begin. Check your telecoms bills and ask your provider to identify any remaining ISDN or analogue services.

It’s worth doing this even if nobody remembers using a particular line. Some connections are rarely thought about because they support equipment rather than everyday phone calls.

What else could be connected to an old phone line?

Your phone system is only part of the picture. Depending on your premises and the age of your equipment, analogue lines may also support:

• Card payment terminals
• Security and fire alarms
• CCTV systems
• Door entry systems
• Lift emergency phones
• Fax machines
• Other monitoring or communications equipment

Some equipment may work with a digital service after being reconfigured. Some may need an upgrade or a different connection altogether. The right answer depends on the device, so speak to the company that supplied or maintains it before making changes to its line.

This matters particularly for equipment you depend on in an emergency. You’ll want to know exactly how it will work after the move and test it properly once the new service is installed.

What will replace ISDN and analogue phone lines?

For everyday business calls, the replacement will generally be a digital phone service. Depending on your needs, that might mean a hosted phone system or another digital calling solution.

The right choice isn’t simply the one with the most features. It should suit how your business actually works. For example:

• Do staff answer calls from one office, several sites or while working remotely?
• Do you need calls to reach different teams or departments?
• Are you happy with your current handsets and call handling?
• Is the internet connection at each site suitable for the service you’re considering?
• What needs to happen to keep your existing numbers?

The switch-off is a useful reason to review these questions, but you don’t need to overhaul everything for the sake of it. The aim is to put the right service in place and avoid disruption.

Can you keep your existing business number?

In many cases, yes. Your business number can usually move with you to a new digital phone service. But if you’ve had that number for years, start the process early.

Your number may have moved between providers or phone systems several times. When it comes to transferring it again, the paperwork may need to identify the provider that originally issued the number — not just the company you pay today. Tracking down that original provider can take time, and getting the details wrong may delay the transfer.

If your number appears on your website, vehicles, signage or marketing materials, let your new provider know from the outset that keeping it is essential. They can help you check the information needed for the transfer and plan the changeover. Don’t cancel your existing service before you’ve confirmed how and when your number will move.

What should your business do now?

1. Make a list of every phone line and ISDN service.
   Start with your bills, then check each premises. Include lines that aren’t used for regular calls.
2. Find out what each line does.
   Speak to the people responsible for your phone system, building, security equipment and payment systems. If you can’t identify a line, investigate it before assuming it’s no longer needed.
3. Check connected equipment with its supplier.
   Ask whether it will work with a digital service and whether it needs to be upgraded, reconfigured or replaced.
4. Review your replacement options and phone numbers.
   Think about your calling needs, your internet connection and how the move will work across all your sites. If you want to keep your numbers, ask your provider to check the transfer details early — particularly for numbers you’ve held for a long time.
5. Plan the change and test it.
   Allow time for installation, number transfers and testing. Check incoming and outgoing calls, and make sure any alarms or other connected devices work as intended.

You don’t have to complete every step in one go. The important thing is to start early enough to deal with anything unexpected.

Why act now if the deadline is in January?

It’s tempting to put this on a list for later. But the more lines, sites and suppliers involved, the more there is to coordinate. You may discover equipment that needs replacing, or that tracing the history of a long-held phone number takes longer than expected.

Leaving enough time gives you the chance to make decisions based on what your business needs, rather than rushing to keep a service running as the deadline approaches.

And if you’ve already moved your main phones to digital? A quick check of any remaining lines is still worthwhile. It’s often the less visible connections that are easiest to miss.

How TST can help

If you’re not sure what services your business has or where to begin, TST can help you make sense of it. We can review your current telecoms setup, help identify lines that need attention and talk through suitable options for moving your business calls to digital. We can also help you plan ahead if you need to keep your existing numbers.

The first step is simply finding out what you’re using today. Get in touch with TST and we’ll help you work out what needs to happen before 31 January 2027.