Openreach is retiring the UK’s legacy copper voice network (PSTN/WLR and ISDN), with national switch-off planned by 31 January 2027. Many areas will need to migrate sooner due to “Stop Sell” and fibre upgrade milestones, so it pays to plan ahead.
PSTN Lines (Public Switched Telephone Network)
Around for over 100 years, PSTN lines are a traditional land line that you would typically see at home or in a smaller office. These traditional lines provide the basics for communicating such as Caller ID and Call Divert and are limited to a single telephone number provided by BT.
ISDN Lines (Integrated Services Digital Network)
ISDN lines are Digital Lines and are more common than PSTN Lines in business, as you can have as many channels as you want. Larger businesses with departments tend to opt for ISDN due to the ability to provide DDI (Direct Dial) numbers for employees/departments. Calls can also be transferred to external numbers and includes Caller ID so users can see the number of the person calling them before they answer the phone.
SIP Lines (Session Initiation Protocol – VoIP)
By 2027, BT Openreach will have switched off both PSTN and ISDN lines moving everyone onto VoIP/Internet Telephony. SIP uses an the internet to connect a phone system to the telephony network provider. You still have access to all of the features provided by an ISDN line, with the added benefit of not being tied to any BT exchange,. This means you can select your own phone numbers with any Local STD code and display this when calling out.
As SIP Lines connect via an internet connection making SIP considerably cheaper than any landline type. It also provides increased flexibility and better Disaster Recovery solutions. The quality of the calls is related to the quality of the internet connection so you may need to upgrade your internet package, but over all VoIP is the way forward and BT Openreach are forcing the transition.
Why act now (not in 2027): while the national retirement date is 31 January 2027, the migration timetable is effectively being pulled forward in many locations as fibre becomes the default and legacy services are progressively constrained. The safest approach is to identify every line-dependent service (phones, alarms, lifts, EPOS, door entry, fax, PDQs) and schedule a controlled move to IP voice, resilient connectivity, and backup routing—well before the deadline.
Start with our PSTN switch-off hub: — then contact us and we’ll map your lines/devices and the quickest migration route.
