Is Your Business Still on ISDN? The Clock Is Running Out.

BT's Public Switched Telephone Network (PSTN) and ISDN switch-off is one of the most significant changes to UK business communications infrastructure in decades. By the end of 2027, the traditional copper telephone network will be switched off entirely. If your business phones, alarm systems, door entry systems, or card payment terminals still connect via traditional lines, you need a plan.

What Is Actually Being Switched Off?

The PSTN is the traditional analogue telephone network that has been in place for over a century. ISDN (Integrated Services Digital Network) sits on top of the PSTN and provides the digital phone lines that most businesses have used for the past 30 years. Both are being retired.

From January 2027, Openreach will cease providing PSTN and ISDN services to new customers. Full switch-off is planned for December 2027, at which point all existing services will stop working.

This is not a recommendation. It is an infrastructure shutdown.

What Replaces PSTN and ISDN?

The replacement is Voice over IP (VoIP), also called hosted telephony or cloud telephony. Instead of calls travelling over dedicated copper lines, they are carried over your internet connection as data. The experience for users is the same: pick up a handset, dial a number, have a conversation.

The difference is in the infrastructure. VoIP systems are hosted in the cloud, managed via a web portal, and can be accessed from physical handsets, desktop softphones, or mobile apps. For most businesses, the move to VoIP is also an opportunity to rethink how their phone system works.

What Else Might Be Affected?

Voice calls are the obvious concern, but PSTN and ISDN connections are used for other things that are easy to overlook.

• Alarm systems: Many intruder and fire alarm systems use a PSTN line to dial out to a monitoring centre. These will stop working at switch-off.
• Door entry and access control: Older intercom systems often rely on traditional phone lines.
• Franking machines: Some franking machines connect via PSTN to update postage rates.
• Lifts: Emergency telephone systems in lifts frequently use analogue lines.
• CCTV and remote monitoring: Older systems may connect via PSTN for remote access.

A full audit of which systems in your building use traditional lines is essential before your migration date.

What Should You Do Now?

The businesses most at risk are those that leave the migration to the last minute. Demand for VoIP installation will increase significantly as the deadline approaches. Installation capacity will become stretched, lead times will grow, and costs will likely rise.

The sensible approach is to audit your current connections now, understand what needs replacing, and plan the migration at a time that suits your business rather than being forced into it under pressure.

For most businesses, migrating to a hosted VoIP system is straightforward. Modern VoIP systems are flexible, scalable, and often cost less per month than the equivalent ISDN lines. The migration is also an opportunity to add features, such as call recording, auto-attendant menus, and mobile integration, that were either unavailable or expensive on traditional systems.

What to Look for in a VoIP System

When evaluating VoIP providers, the key questions are: What happens if the internet goes down? How is the system managed and updated? What hardware is required at your premises? Is call quality monitored and guaranteed?

Quality of service (QoS) configuration on your network is important. VoIP is sensitive to latency and packet loss in a way that email is not. Your internet connection and internal network need to be assessed to ensure they can support the call quality your business needs.