The UK’s traditional phone network is being switched off for good. By 31 January 2027, BT will retire the Public Switched Telephone Network (PSTN), ISDN, and ADSL, the analogue infrastructure that has carried UK business communications for decades. For SMEs, this is one of the most significant infrastructure changes in a generation, and many simply aren’t ready for it.
What is the PSTN switch-off?
In plain terms, BT is ending its copper-based phone network and moving every service onto IP, meaning calls and connections run over the internet rather than physical copper wire. New orders for these legacy services already stopped nationwide in September 2023, so any change to an existing line now defaults to a digital alternative. The full switch-off is set for January 2027, but migration is already happening exchange by exchange across the country.
It’s not just about your phones
This is the part most businesses underestimate. Traditional phone lines also carry services like alarms, EPOS machines, door entry systems, CCTV, and fax machines. ADSL and some FTTC broadband connections rely on the same copper network, so they’re affected too. If your business hasn’t fully audited what’s actually running over these lines, the switch-off could catch you out somewhere unexpected.
What happens if you don’t act
Any service still running on PSTN or ISDN after 31 January 2027 will simply stop working. Nothing migrates automatically for every service type. Lines left unmigrated may fall back to Emergency Voice Access, which only supports emergency calls and won’t carry broadband or device signalling. Waiting also has a direct cost: Openreach has confirmed staged price rises on legacy line rentals through 2026, roughly doubling annual costs by autumn. The longer a business leaves it, the more expensive and disruptive the eventual cutover becomes.
Why this is actually an opportunity
Legacy phone systems are typically costly to maintain and limited in what they can do. Ofcom’s Connected Nations report found a 45% increase in significant PSTN resilience incidents in 2024 alone, a sign of just how fragile the ageing infrastructure has become. A forced migration is the right moment to move to something genuinely better: VoIP, UCaaS, and cloud telephony all offer more flexibility, better reliability, and often lower running costs than what they replace.
What a well-managed migration looks like
A good migration follows four steps. First, an audit of every service and piece of hardware currently running over PSTN lines. Second, an honest assessment of what your business actually needs from its communications going forward. Third, implementation of the right IP-based replacement. Fourth, a managed cutover that preserves your existing numbers and capability without disruption to day-to-day operations.
How 4th Platform helps
We audit your current exposure across phones, broadband, and every connected device that depends on the old network. We design and implement the right replacement for your business, then manage the migration end to end, including number porting, hardware replacement, and testing. The result is a system that integrates cleanly with the rest of your technology stack, with no surprises on switch-off day.
Start the conversation now
January 2027 feels distant until it isn’t. Migration takes planning, and the businesses that start early get the most options and the smoothest transition. If you haven’t begun yours, now is the time.
Speak to 4th Platform about your switch-off readiness →
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