The PSTN switch-off is the process of shutting down the Public Switched Telephone Network (PSTN), which is the traditional copper-based telephone network. The PSTN is being replaced by a new digital network called Voice over Internet Protocol (VoIP). The PSTN switch-off is scheduled to take place in the UK in December 2025. This means that businesses that currently use PSTN-based services, such as landlines and ISDN lines, will need to switch to a new digital solution by that date.