What Is PSTN? The Public Switched Telephone Network Explained

PSTN stands for Public Switched Telephone Network. It's the traditional copper-wire phone network that has carried landline calls for decades.

How PSTN Works

PSTN uses physical phone lines (copper) to connect calls. When you dial a number, the call is routed through local exchanges and long-distance networks until it reaches the destination.

The UK PSTN Switch-Off

Openreach is switching off the PSTN on 31 January 2027 — the original December 2025 date was pushed back to protect telecare users, and Openreach confirmed in July 2026 that there will be no further extension. All landlines move to digital (IP) technology. In July 2026 around 1.5 million lines, including roughly 350,000 business premises, were still on the old network. Residential single lines that miss the date get a temporary voice-only fallback (Emergency Voice Access); business lines do not, so businesses need to migrate to VoIP or a digital line before the deadline.

PSTN vs VoIP

VoIP sends calls over the internet instead of copper lines. It's more flexible, often cheaper, and supports features like video and integration with business software. Migrating from PSTN to VoIP is the recommended path for most businesses.