This page has been updated. The ISDN switch off did not complete in December 2025. Openreach extended the deadline, and the analogue network now shuts down permanently on 31 January 2027.
For the current position, including the 2026 price rises on legacy lines and what happens to alarms, lifts and card machines, read our full guide: The Big Switch Off: what the January 2027 landline shutdown means for your business.
What is ISDN?
ISDN stands for Integrated Services Digital Network. It is a digital line that runs over copper wiring, and it was considerably faster than the traditional analogue lines that came before it, carrying both data and voice calls. Its weakness is that it depends entirely on physical copper infrastructure, which is expensive to maintain and increasingly difficult to repair.
Why the date moved
Openreach announced back in 2015 that it would stop selling ISDN in 2020 and switch the network off in 2025. The stop sell happened as planned in September 2023, and no new ISDN or analogue lines have been available since.
The final shutdown, however, was pushed back. In 2024 the deadline moved from December 2025 to 31 January 2027, largely to allow more time to migrate vulnerable users and telecare devices safely. That extension is the reason this page needed rewriting.
The new date is fixed. Openreach has been clear it will not move again, and exchanges are already being migrated in phases, so many businesses will lose analogue service before January 2027 rather than on the day itself.
What to do if you still have an ISDN line
You need to migrate to a digital service, which in practice means VoIP. Your existing numbers can be ported across, so nothing changes for your customers.
Two things are worth knowing. First, VoIP depends on your internet connection, so if your broadband is also running over the old copper network it makes sense to upgrade both together. Second, it is not only phones that are affected. Alarm panels, lift emergency lines, door entry systems and older card terminals all commonly sit on analogue lines and need their own migration path.
Legacy line rental is also rising steeply through 2026 in three separate wholesale increases, so staying on copper is now the expensive option as well as the one with a deadline attached.
Get help before the deadline
We migrate businesses across West Sussex from ageing ISDN and analogue setups onto modern hosted phone systems, handling the audit, the number porting and the connectivity as one project.
Call 01903 255 159 or read the full Big Switch Off guide to see what applies to you.