The era of ISDN is drawing to a close, with BT announcing that it will no longer sell new networks from 2020, aiming to completely shut off all ISDN and PSTN circuits by 2025. This means if you’re still using the old legacy technology, then you need to prepare for the switch or risk getting left behind.


First, let's unpack the jargon. PSTN is the Public Switched Telephone Network: the system that carries analogue voice data over copper lines. It enables landlines to operate and has been around in some capacity since the 1800s.

ISDN stands for Integrated Services Digital Network. It was first introduced in the 1980s as the successor to dial-up technology, supplying voice and data simultaneously over traditional PSTN circuits.

The two systems have worked in blissful harmony for years, and over two million businesses still utilise this technology as part of their communications... But technological advancements have made modern methods more intuitive, easier to maintain, and much, much faster. While we thank them for their service, by 2025 these traditional voice, alarm, and broadband solutions will be switched off.


The transition to alternative solutions has already begun, with Voice over Internet Protocol (VoIP) as ISDN's main successor - essentially a phone service delivered over the internet. Unlike ISDN, VoIP only requires an internet connection to run, removing the need to have costly old-fashioned phone lines across your business. Other benefits involve better call quality, higher flexibility, and more features than traditional ISDN lines.

There's also Session Initiation Protocol (SIP), which connects to most existing systems as a legacy upgrade, making it a popular choice for those moving over to an internet-based network. SIP-trunks allow you to use VoIP by connecting your phone system to the public phone network from an Internet Protocol (IP) system. In any case both offerings are a substantial upgrade from ISDN, giving you more control over your network through IP.

So, now that we’ve explored the replacements, here’s how to prepare your business for the upcoming switch off.


It's crunch time. With the Stop-Sell having already begun in some areas, essentially meaning that any new or changes to existing ISDN, PSTN or associated broadband and Fibre to the Cabinet (FTTC) services will no longer be provisioned. These services are actively being withdrawn from December 2022, and if alternative technologies are not implemented businesses may face disruption

So, how can protect and empower your business?

1. Don't Renew Your Current Contract

The first phase of the switch off is upon us, so it’s better to begin the shift towards a more modern system like VoIP than keep renewing one that will soon be obsolete.  So, look for the earliest time you can make the switch and start researching the best solution for your business.

2. Choose Your Replacement

Your specific requirements will vary, and your decision will typically be dictated by the size of your business.

Although both are well equipped for scalability, VoIP is better suited to small businesses due to its easy installation. SIP lets you keep your existing phone system if you want to avoid the hassle of replacing it, which makes it better suited to larger businesses with different branches and better IT support.

Both systems are great improvements from ISDN - you just need to find out which one best suits your business.

3. Check Your Existing Systems

Before you start out with your new solution, you need to make sure you’ve got the functionality for it. Your internet has to be up to speed (literally…) and have an adequate amount of bandwidth to handle your calls.  

You also need to check that your current system can support the upgrade. The majority of systems are compatible with VoIP and SIP, but we recommended double-checking that yours is before you move over. If you’re only equipped for ISDN, then it’s time for an upgrade across the board. Use this opportunity to discuss the future of your communications, so you can be well-equipped going forward.

4. Install & You’re Ready to Go

Once you’ve chosen a solution and checked it can integrate with your system, then you’re ready to roll it out across your business!

Installation can take as little as three weeks but will vary from company to company based on factors like size, users, and the number of locations. Once you’re all set up you can rest easy, knowing your business is future-proof.


Here at Intercity, we're experts in communications and technology services. We're perfectly positioned to help you manage all aspects of your migration from ISDN to VoIP. As trusted partners, we'll work with you through the whole journey - and beyond.


Get ready for the switch-off by downloading our free Product Stop-Sell List to find out when your business will be affected or give us a call on 0330 331 7933 to talk with one of our PSTN ISDN specialists so that you can switch-off your worries about the network changes now!