Publish Date
14/05/2026
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The PSTN switch off UK deadline is no longer a distant technical milestone. It now has a firm timeline, a wide-reaching impact, and real consequences for organisations that delay action.
By 31st January 2027, the UK’s legacy Public Switched Telephone Network (PSTN) and ISDN services will be permanently retired. After this point, any service still running on copper-based phone infrastructure will stop working entirely.
Despite years of warnings, it’s estimated that 60% of UK organisations still rely on PSTN or ISDN in some form. That leaves a significant proportion of businesses at risk of disruption if they don’t act in time before the switch off.
What is the PSTN switch off?
The PSTN switch off refers to the nationwide retirement of the traditional copper telephone network that has supported landlines for decades. This network is being replaced with digital, IP-based services such as VoIP (Voice Over Internet Protocol) and cloud telephony.
While PSTN is often associated with phone systems, the impact goes far beyond voice calls. Many business-critical services still rely on PSTN lines, including:
- Alarm and security systems
- Payment terminals and EPOS
- Lift emergency phones
- Fax machines and legacy devices
- Broadband services tied to copper lines
Any of these will stop functioning after January 2027 if they are not upgraded.
How many UK businesses are affected?
The scale of the PSTN switch off UK is often underestimated, with millions of homes and businesses still connected to the copper network (around 14 million premises affected overall). At the same time, Openreach has confirmed that hundreds of thousands of business lines still need to migrate as the deadline approaches.
This means many organisations are either:
- Still fully reliant on PSTN/ISDN
- Running hybrid environments
- Unaware of how many systems depend on legacy lines
Why the PSTN switch off UK deadline matters
The PSTN switch off in the UK is not a phased coexistence model. Once the network is retired, it’s gone.
Any systems still dependent on PSTN or ISDN will simply stop working.
Alongside the hard deadline, businesses are already facing:
- Service restrictions due to the national “stop sell” policy (no new PSTN services)
- Rising costs as providers increase pricing to accelerate migration
- Operational pressure as demand for migration services increases nearer the deadline
In practical terms, delaying action creates these three key risks:
- Service disruption when legacy infrastructure is removed
- Cost pressure as line rental increases
- Rushed migration leading to poor implementation decisions
The need to prepare
If no action is taken before the PSTN switch off UK deadline, affected services won’t degrade, but rather they will stop, leading to difficulties around:
- Customer communication channels
- Payment processing
- Safety systems (alarms, lifts, monitoring)
- Internal operations reliant on legacy lines
For many businesses, the issue isn’t their main phone system; it’s the hidden dependencies connected to PSTN.
What to do and how to prepare for the switch off: Modern telephony
This is a new opportunity for most organisations to modernise their communication systems. Cloud-based phone solutions like Microsoft Teams Phone allow businesses to:
- Replace traditional phone systems with IP-based calling (calling over the internet)
- Integrate voice, chat, and collaboration in one platform
- Support hybrid and remote working
- Remove reliance on on-premises PBX (Private Branch Exchange) hardware
Crucially, migration doesn’t need to happen all at once. Businesses can:
- Transition in phases (perfect for testing)
- Retain existing numbers through porting
- Integrate with existing SIP or telephony environments
This approach reduces risk and avoids last-minute disruption.
The reality: 2027 will come quickly
The PSTN switch off UK deadline is fixed. There are no extensions expected, and the process is already well underway. Organisations that act early benefit from:
- Greater flexibility in solution choice
- Controlled, phased migration
- Stable costs and timelines
Those that delay are more likely to face:
- Limited supplier availability
- Time pressure
- Increased costs and disruption
Final Thoughts
The PSTN switch off in the UK is one of the biggest changes to UK telecommunications in decades. It affects far more than traditional phone lines and requires careful planning.
For businesses, this isn’t just about replacing old technology, but rather about ensuring continuity, reducing risk, and aligning communications with a modern, cloud-first way of working.
If you’d like a hand preparing for the PSTN switch-off and transitioning to a more modern telephony setup, our team is happy to help. Just fill out our contact form here and we will be in touch!