PSTN is the traditional phone line system. It’s used in two ways – to provide a home phone service and broadband. It’s scheduled to be switched off in 2027, by this time all homes should have access to fibre optic broadband and Voice over Internet Protocol (VoIP). Most customers won’t be affected by the switch, however vulnerable customers who rely on telecare alarms could be left without emergency care if not provided with a back-up battery for alarms.