ISDN Switch Off UK: Key Dates, Deadline & What to Do

Last updated: July 2026

Key facts at a glance: ISDN and traditional phone lines are being retired across the UK. No new ISDN lines have been sold since 2023, and full migration must be completed by the end of January 2027. Businesses still relying on ISDN need to move to VoIP or SIP before then to avoid losing phone service.

What is ISDN?

ISDN stands for Integrated Services Digital Network. It’s a set of communication standards for transmitting digital data and voice over traditional telephone lines. ISDN was developed to provide a more efficient, higher-quality alternative to the analogue telephone systems that came before it. It has since been overtaken by newer technologies like broadband internet and Voice over Internet Protocol (VoIP), which offer faster speeds and more flexible ways of communicating.

Why is ISDN being switched off?

Openreach is retiring the ageing copper telephone network that ISDN depends on, in favour of full-fibre and internet-based infrastructure. As the network winds down, support for ISDN is disappearing too: engineers are less able to fix faults, and replacement parts are becoming harder to source. Because of this, ISDN is being switched off, and any UK business still using it will need to upgrade to a newer system before the cut-off date.

When does it switch off?

Operators in the UK stopped installing or adding ISDN lines in 2023. Since 5th September 2023, Openreach have ceased providing new landlines to customers in the UK – this applies to homes and businesses.

The date of the ISDN forced migration is the end of January 2027.

What happens if you don’t switch before the deadline?

After the deadline, ISDN will no longer be supported: there will be no fault-fixing, and replacement parts will no longer be available. Businesses that leave their migration too late are likely to face a long queue for installations, which could leave you without a working phone system for a period of time. It’s important to plan your switch well ahead of the deadline, rather than waiting until the last minute.

Your alternatives to ISDN

SIP trunking

SIP (Session Initiation Protocol) trunking lets you keep your existing on-site phone system (PBX) but connects it to the internet instead of a traditional line. It’s a good option if you’ve already invested in PBX hardware and want to keep using it while moving your calls over to broadband.

VoIP (Voice over Internet Protocol)

VoIP is a cloud-based phone system that lets you make and receive calls entirely over the internet, without needing on-site PBX hardware. It’s typically more flexible than SIP, and often bundles in features like video calling and instant messaging as standard.

Find out more in our guide to PBX and VoIP systems.

How to prepare for the switch off

Check what phone system you currently have and whether it relies on ISDN or PSTN lines.
Assess your business broadband connection, since your new system will depend on it.
Compare SIP and VoIP against your business’s needs, such as whether you want to keep existing hardware.
Book your migration in good time, rather than waiting for the pre-deadline rush.
Speak to a business communications provider, like Wayv, for advice tailored to your setup.

Frequently asked questions

When is the ISDN switch off deadline?
The final deadline for migrating off ISDN in the UK is the end of January 2027.

Will my phone number change if I switch?
No — in most cases, your existing phone numbers can be ported over to your new SIP or VoIP system.

What’s the difference between SIP and VoIP?
SIP connects your existing on-site phone system to the internet, while VoIP is a fully cloud-based system that doesn’t require on-site hardware.

Do I need new hardware to switch?
It depends on the option you choose. SIP often lets you keep your existing PBX hardware, while VoIP is cloud-based and may require new handsets or devices.