31 January 2027: Is Your PSTN Migration on Track?
October 28th, 2026
The UK’s communications landscape is undergoing one of the biggest changes in decades. After years of supporting business telephony, the Public Switched Telephone Network (PSTN) and Integrated Services Digital Network (ISDN) are being retired as the UK’s communications infrastructure moves to IP-based services.
What is the PSTN and ISDN switch off?
The Public Switched Telephone Network (PSTN) has been the foundation of voice communications in the UK for decades. For many organisations, PSTN connectivity is delivered through ISDN services, connecting their phone systems to the wider public telephone network.
For years, these services have provided reliable connectivity with little need for day-to-day attention. However, the infrastructure that supports PSTN and ISDN is ageing and increasingly difficult to maintain. As a result, Openreach is retiring the UK’s legacy PSTN network and moving communications services to modern IP-based alternatives.
This means organisations still using PSTN and ISDN services must migrate to alternative technologies before legacy services are permanently withdrawn. With the final switch off now only a matter of months away, organisations that have not yet started planning their transition should take immediate action.
When is the switch off happening?
The PSTN and ISDN switch off is now entering its final stages, with organisations running out of time to plan and complete their migration.
📅 31 January 2027: number porting order in place
📅 End of March 2027: porting complete
Organisations that still rely on PSTN or ISDN services should aim to have a number porting order in place by 31st January, with porting completed by the end of March 2027. As the deadline approaches, demand for migration and porting services is expected to increase, making early planning essential to avoid delays, secure the necessary resources and ensure a smooth transition to IP-based communications.
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Many organisations have already completed their migration, but we’re still speaking to those that rely on legacy PSTN and ISDN services. With the final deadlines now approaching, organisations that have not yet started planning should act quickly. Leaving it too late could significantly reduce the options available to ensure a smooth and successful transition. |
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| Jono Darlington
Senior Solutions Architect, Cinos
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Alternatives to ISDN
With the switch off deadline fast approaching, organisations should now be evaluating their migration options. For most, the replacement for ISDN comes in the form of SIP Trunking.
SIP Trunking provides the same PSTN connectivity, but rather than being delivered over a physical copper cable, calls are carried over an IP network. It will still provide those inbound and outbound calls in exactly the same way that ISDN has but also allows for additional features and greater resilience than traditional telephony.
Switching to SIP Trunking gives organisations the option to futureproof their existing hardware and make it compatible with internet enabled telephony solutions. Once the PSTN is switched off, legacy telephony equipment that relies on these services will need an alternative means of connectivity. So, if organisations are keen to keep their current equipment, then opting for SIP Trunking is essential. Not only will this allow them to take advantage of integrated communications, including messaging, presence, and video, it will enable organisations to integrate infrastructure across voice, connectivity, and security, providing a robust network for both internal and external communication.
What the switch off means for NHS trusts and blue light services
While every organisation must prepare for the PSTN switch-off, the implications are particularly significant for NHS trusts, hospitals and blue light services where communications are often mission-critical.
Many healthcare and emergency service environments still rely on legacy telephony systems that have evolved over many years and support essential operational and emergency workflows. These services cannot simply be switched off and replaced overnight.
The challenge is not only technical. Organisations must preserve continuity of service, maintain resilience, manage risk and ensure communications remain available when they are needed most. After all, any disruption could impact patient care, operational response and public safety.
For many organisations, the complexity lies not just in replacing legacy services, but in understanding how deeply embedded they have become within critical day-to-day operations.
Critical calling environments
Nowhere is this challenge more apparent than in critical calling environments, where telephony services often support workflows that cannot tolerate interruption or downtime.
Healthcare organisations provide a strong example. Many hospitals continue to use dedicated analogue “Red Phone” services for emergency communications, including crash calls and other critical workflows. These systems have earned trust through years of reliable service, making any change understandably sensitive.
A common concern is that moving away from traditional PSTN infrastructure introduces additional risk. In reality, modern SIP solutions can often improve resilience when designed correctly. Unlike fixed legacy circuits, SIP services can reroute traffic in response to connectivity issues, helping maintain service availability when faults occur.
However, technology alone is not enough. Successful migration requires careful planning, clear ownership and experienced project delivery. Number migrations, service continuity, resilience design and stakeholder management all play a crucial role in ensuring a smooth transition.
The Cinos SIP Trunking Service
As organisations move closer to the PSTN switch-off deadline, choosing the right migration partner is just as important as selecting the right technology. Cinos brings extensive experience in managing communications migrations for critical environments, supporting organisations including police forces, acute NHS trusts, hospitals and central government departments.
We specialise in delivering resilient SIP PSTN services for organisations where uninterrupted voice communications are essential, alongside carefully planned migrations designed to minimise risk and disruption. Our service supports connectivity into traditional on-premise PBXs as well as cloud communications platforms such as Microsoft Teams and Cisco Webex Calling.
As a Tier 1 SIP Service Provider, Cinos delivers its own SIP PSTN service without reliance on third-party providers, giving customers a single provider relationship and end-to-end ownership of the solution.
At the heart of the service is Cinos Cloud, our Cisco-powered communications platform hosted within UK data centres. It combines resilient SIP services with flexible connectivity options, including internet connectivity, HSCN networks, private circuits and MPLS services, providing the robust foundation needed for business-critical and mission-critical communications.
We also manage number porting activities on behalf of customers, helping to simplify migration and minimise disruption.
Don’t Leave Your PSTN Migration Too Late
The PSTN and ISDN switch-off may be approaching its final stages, but organisations still have time to act.
The key is not waiting until the deadline is here. Early planning reduces risk, simplifies migration and helps ensure you have access to the expertise and resources needed to complete the transition successfully.
If your organisation still relies on PSTN or ISDN services, now is the time to review your communications environment and put a migration plan in place before demand increases and migration windows become more limited.
Speak to Cinos today to discuss your PSTN and ISDN migration strategy and discover how our SIP Trunking services can support a smooth transition to a future-ready communications platform.
