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BT is switching off the UK's Public Switched Telephone Network (PSTN), with the national transition set to complete in 2027. Any business still using traditional phone lines or services that depend on them needs to be ready before then, with 2026 being the final year to prepare. The change affects organisations of all sizes and requires a review of any services still running over legacy phone lines to ensure continuity.
PSTN is the UK's legacy phone network and uses copper lines to carry voice calls and older connectivity services. It has reliably supported businesses for decades, but it was not designed for today's internet-based ways of working.
The switch-off also includes other legacy services such as ISDN, which some organisations still use for voice and data. As these services are retired, Openreach is moving the UK to all-IP networks, where calls and related services run over a broadband connection rather than a traditional phone line.
The important point for businesses is this: PSTN and ISDN don't just support phones. They can also sit behind systems that quietly rely on a copper line, including:
Identifying these dependencies early is the first step to avoiding disruption during the transition.
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When PSTN is switched off, phone services and other connected systems no longer operate independently of your internet connection. Instead, they become part of your wider data network, which changes how reliability and resilience need to be planned.
In practical terms, this means:
These changes don't make communications less reliable, but they do require a different approach. Reviewing how your voice, data, and connected systems work together helps ensure critical services continue to operate as expected.
For many businesses, the biggest risk isn't the switch itself; it's not knowing what's still connected to an old phone line until something stops working. That's why it's worth reviewing your current setup now, while you still have time to plan the move properly.
If PSTN-based services are still in place when the national switch-off happens, remaining lines may be moved to a basic fallback called Emergency Voice Access (EVAC). EVAC is intended as a last-resort safety net and supports emergency voice calls only.
It won't support everyday business services such as:
The simplest way to avoid disruption is to check what you're using today and schedule the right upgrades before the deadline. A short review can highlight any hidden dependencies and help you move to digital services with minimal change for your team.
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Treken supports businesses across Dorset and Hampshire with reliable IT, cloud, and communications support. If you're unsure how the PSTN switch-off will affect your setup, we can help you assess what's in place and plan a smooth transition to IP-based services that protect day-to-day operations.
To speak with a member of our friendly team, call 01202 612333.
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