An Openreach tech told me last week that while the PSTN telephone system (i.e. the currently used switching and connecting system for telephony) will be phased out (2025 is the currently projected 'date' (year to be pedantic, but you know what I mean!)), it's very unlikely the copper lines running into homes, workplaces, etc themselves will be taken out of service.
It's just the telephone signal will be converted to internet protocol and sent&received via the internet connection, but that internet connection can still be sent down a metallic conductor line. Of course, if someone has fibre to the home/premises (FTTH/FTTP) internet then the telephone data will be converted and sent/received via the fibre.
People with alarms etc that use the current PSTN will need to have the systems adjusted/altered/upgraded, of course.
I think what's happened is that the arrival of FTTH/FTTP has been conflated with the switch off of PSTN; people are thinking that PSTN being switched off means all the metallic wires are going to be ripped out as part of that drive. Not likely according to the Openreach tech.
