What’s the ISDN/PSTN switch-off?
BT is retiring the infrastructure that supports landline phones. They’re installing a more advanced digital network in its place, and all calls will be routed over IP (internet protocol).
This is already under way. As of 5th September 2023, BT Openreach is no longer selling products based on this legacy technology, and in many parts of the country the old lines are shut down. This will be complete nationwide by 2025.