What it actually means
PSTN stands for Public Switched Telephone Network. It's the copper analogue system that has carried UK phone calls for decades, and Openreach is shutting it down. The stop sell already happened, which means providers can no longer order new copper lines or upgrade existing ones across most of the country. Full retirement is scheduled for January 2027.
Every phone line that still runs over copper has to move across to a digital voice service, sometimes called VoIP, that runs over your broadband instead. Your number stays the same. Your handset usually stays the same too, although older devices like alarm pendants, lift phones, care lines, fax machines and some payment terminals may need replacing or reconfiguring because they were built to talk to the old copper signal.
At home
What this looks like in the house
If you've ever assumed the landline in the hall would always just work, the switch off is the moment that assumption breaks. The classic scenario is an older relative with a fall pendant that dials a monitoring centre over the copper line. One day the line gets migrated, the pendant tries to dial out, and nothing happens. Or the kids pick up the handset to call grandma on a Sunday evening and get silence. It isn't a failure, it's an industry change that nobody warned the household about properly.
In business
What this looks like at work
For a small business the felt cost is money walking out of the door. A card machine that still runs over the analogue line stalls mid transaction at the till. The lift phone fails its next safety inspection because it can't reach the monitoring company. An inbound sales call hits a dead tone because the line was migrated overnight and the new digital service was never set up. Every one of those is real revenue lost, plus the goodwill of a customer who tried to reach you and couldn't.