PSTN is a privately-owned copper wired based telecoms network and the decision to upgrade it has been taken by the telecommunications industry. Fixed-line operators - such as Openreach, BT and Virgin MediaO2 - will replace analogue telephone services with Voice over Internet Protocol (VoIP) technology, which carries voice calls as data using internet technology. The upgrade will be delivered by the telecoms industry in a phased approach over the next couple of years, with the UK network expected to be fully upgraded to VoIP services in 2025. The switchover will happen on a telephone exchange by exchange basis and not on a regional basis seen in relation to the switchover of analogue television.

Public Switched Telephone Network - this term is used to either describe the entire analogue telephony network in the UK or a specific analogue telephone line connected to a property.

The 'traditional' telephone network that is now being replaced with IP based signalling systems. It is largely based on voice and DTMF/STMF signals.