Everything You Need to Know About the ISDN Switch Off (Updated 2025)

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The UK’s phone network is undergoing a major transformation. Legacy systems like the Integrated Services Digital Network (ISDN) and the Public Switched Telephone Network (PSTN) are being phased out in favour of modern, digital alternatives. This shift will affect both homes and businesses, and it’s crucial to be prepared.

What is the ISDN Switch Off? 

The ISDN Switch Off refers to the nationwide retirement of the PSTN and ISDN networks. Initiated in 2020, this process is part of a broader move to fully digital communications. While the original target for complete switch-off was December 2025, the final deadline has now been extended to January 2027

Why is the ISDN Switch Off Happening?

ISDN, introduced in the 1980s, was once cutting-edge. However, it can no longer meet the demands of today’s digital-first world. The network is outdated, inflexible, and expensive to maintain. With the rise of remote work, cloud services, and high-speed internet, digital solutions like VoIP (Voice over Internet Protocol) offer far superior performance, scalability, and cost-efficiency.

What Will Replace ISDN?

ISDN and PSTN services are being replaced by IP-based digital phone lines. These use broadband connections to transmit voice and data, enabling features like:

• VoIP phone systems (hosted in the cloud)
• Full fibre broadband for faster, more reliable connectivity

What Are the Key ISDN Switch Off Dates?

• September 2023: Sales of PSTN/ISDN-related products ceased nationwide.
• December 2025: Businesses are advised to complete their migration by this date.
• January 2027: Final switch-off of all PSTN and ISDN services

What Does Your Business Need to Do Before the ISDN Switch Off?

1. Audit your current systems: Identify any services still using PSTN or ISDN (e.g., alarms, fax machines, EPOS).
2. Choose your upgrade path:  Fully cloud-based, flexible, and scalable.
3. Check compatibility: Ensure your hardware supports IP-based services.
4. Plan early: Avoid disruption by migrating well before the 2027 deadline.

Support for Vulnerable Users

The UK government and telecom providers have introduced charters and safeguards to protect vulnerable users during the transition. If your business supports telecare or critical services, consult the Telecare National Action Plan for guidance.