fundamentals
Public Switched Telephone Network. The PSTN is the traditional copper and fibre phone network that has connected landlines for over a century. VoIP systems still reach PSTN numbers, but the call typically converts to internet data at some point in the journey.
The PSTN is the original global phone network: physical wires, exchanges and switches built up since the 1800s. Every landline and most older business phone systems connect through it, using circuit-switched connections rather than internet packets.
Today, few calls travel the PSTN end to end. A VoIP call to a landline usually rides the internet most of the way. Then it converts to PSTN signalling at a gateway near the destination. The caller never notices the handoff.
Countries are actively retiring parts of the PSTN. The UK is switching off its old analogue network by 2027. The US has seen carriers phase out copper lines for years, pushing almost everyone toward VoIP-based alternatives regardless of preference.
Worked example
A UK accountancy firm still has an old analogue phone line installed in 2015.
With the national PSTN switch-off landing by 2027, the firm needs to move to a VoIP-based system before then, since Openreach will stop supporting analogue lines entirely.
Why it matters to a small team
Small businesses still running an old analogue or ISDN line should plan a move to VoIP before their carrier forces the switch. UK and other markets are actively retiring the PSTN, and support windows are closing faster than many expect.
Large parts of it, yes. The UK plans to fully retire its analogue PSTN by 2027, and several other countries are following similar timelines. Existing landlines need to move to VoIP or fibre-based alternatives before their local switch-off date.
PSTN is the traditional circuit-switched copper phone network, while VoIP sends calls as data over the internet. A VoIP call to a landline typically converts to PSTN signalling only at the very last stretch, near the destination number.
Yes. Any reputable VoIP provider connects to the PSTN so calls can reach landlines and mobiles as normal. The caller and receiver notice no difference in how the number looks or how the call is answered.
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