UK fiber broadband provider Openreach has sounded the alarm over the upcoming PSTN switch-off.

PSTN stands for the Public Switched Telephone Network. It is the traditional analog network in the UK that uses copper cables to carry landline voice calls between users.

However, PSTN’s time is coming near to its end as copper is being ditched for the quicker, more energy-efficient fiber offering.

It’s been almost a decade since Openreach announced plans back in 2017 to shut down its PSTN and ISDN networks by the end of 2025 – a date later shifted back to January 31, 2027 – and transition to a single all-digital Internet Protocol (IP) fiber network.

Since that announcement, Openreach said it’s supported the migration of around 15 million lines off the old copper-based network.

While that represents a significant amount, the job is not yet done, as noted by Openreach in a public warning to those that remain on these services as the countdown ticks below 100 days.

According to Openreach, approximately one million copper-based lines remain active across the UK, including 300,000 within business premises.

This could have risks for businesses, Openreach warned, which said these remaining connections are among the most complex to migrate, “meaning action needs to be taken now to avoid disruption.”

“While standard business phone lines are straightforward to upgrade, legacy circuits connected to specialist infrastructure require deeper investigation, testing, and potential equipment replacement. For example, large multi-site organizations may have multiple suppliers and undocumented legacy circuits, making migrations more complex,” said Openreach.

The company noted that beyond standard landlines, a number of critical systems are still highly reliant on PSTN connectivity, including payment terminals (EPOS), lift emergency telephones, fire alarm comms panels, building access controls, and industrial telemetry.

Openreach said if these systems aren’t upgraded before the end of January, it “poses severe operational, safety, and compliance risks,” which could trigger immediate commercial building closures and cause supply chain delays.

“Businesses and organizations that delay action are making things harder for themselves. The straightforward migrations have largely been completed. What’s left are the complex connections that underpin critical operations, requiring careful planning, supplier coordination, and thorough testing,” said James Lilley, director of All-IP at Openreach.

“We are urging businesses to act now, audit their remaining analog services, and work with their communications provider on a migration plan today.”

In an effort to push businesses off legacy services, Openreach hiked its rental prices for legacy ISDN services earlier this month, while further price rises are in the pipeline from February 2027.

Those that don’t migrate before the deadline may be automatically transferred to EVAc—a limited, temporary, last-resort phone service designed strictly to maintain access to essential calls.

“Where technically possible, Openreach will keep linked broadband services running. However, EVAc is a temporary safety net with limited capacity, and it is significantly more expensive than the modern digital alternatives already available,” said the company.