By 2025 BT will be switching off ISDN/WLR networks across the UK. What does that mean for your business and what should you be doing this year to make sure you aren’t caught out?

ISDN Closure in 2025

Last year (2018), BT announced that 2025 would mark the complete shutdown of the ageing ISDN network. It may seem like a long way off, but if your business in the North West is using ISDN technology, it’s better to start looking at the alternatives now, before the rush.

The UK is following the lead of many other countries who are retiring their legacy technologies. On December 31st 2018, Germany closed down their ISDN network – one of the first to do so.

What happened in the lead up to this switch off was widespread panic, as business realised too late that their legacy data systems were about to go. A number of German businesses who were heavily reliant on their ISDN service were simply not aware of that the change was taking place, or how it would affect them. This drove business owners to make quick and sometimes rash decisions on a technology which can have a long-term costly impact on their sustainability.

The advice to businesses who still use ISDN in the UK is to start your change process now and don’t be caught up at the end of service rush that will swamp the market in 2025.


If your business phone calls are handled by a private automatic branch exchange (PABX) system, they will almost certainly be connected to the telephone network using an ISDN line.

When it was brought in, in the late 80s, ISDN was taken up by many businesses because it allowed a line to be subdivided into channels, each one effectively acting as a separate telephone line allowing multiple calls to be made.

The problem with ISDN is that is if often expensive and if you need to extend your call capacity it can often mean adding additional lines that incur additional costs.


The widespread rollout of fibre optic services means most of ISDN’s advantages have been superseded. By 2025, BT is planning to switch to an entirely IP-based model of voice communication.

Voice over IP (VoIP). VoIP is not new, but it is a proven platform that works exceptionally well for businesses.

If your business has renewed its telephone systems in the last few years, and particularly if you have talked to us at DSUK, it is highly likely that you now have a VoIP system.

IP has been growing steadily in the background, as ISDN drops off, with more and more businesses realising the benefits. You can reduce your line rental because you don’t need as many physical lines, and it is vastly scalable and flexible allowing you to add new lines quickly.

VoIP also integrates with mobiles and with computer systems in a unified communications strategy. This allows for solutions such as hot-desking and off-site working to operate successfully without reducing efficiency.


After 2020, you will no longer be able to buy any systems that use PSTN or ISDN. That’s just a year away, so if your current telephone contract is up for renewal, it’s time to start exploring the benefits of VoIP and SIP technologies.

To move to VoIP, you will need to look at whether your existing internet connection is up to the job. It’s recommended that even for small offices, a fibre connection is required for VoIP to work successfully. Larger offices obviously need more bandwidth, so you may consider upgrading your connectivity to an Ethernet-based solution.

For a full and frank discussion of your possibilities, DSUK is happy to offer an onsite visit to help you make the right and most efficient decision for your needs.


Whether or not the 2025 date is met is by BT is under debate. The final date for complete switch off is dependent on how successful BT’s UK-wide fibre rollout is. Without fibre connectivity, there is no real alternative to the existing ISDN technology.

However, it’s important not to fall behind or get stuck in the past.

In the run-up to Germany’s shutdown, 60,000 telephone lines were being converted each week from old ISDN lines. Our advice is to start the preparations sooner rather than later.