The PSTN Switch-Off Is Now a Business Continuity Issue
*Updated 21 September 2026*
The UK PSTN switch-off is no longer something businesses can leave on a future technology roadmap.
Openreach will retire the traditional Public Switched Telephone Network on 31 January 2027. In July 2026, it estimated that approximately 1.5 million lines remained on the old network, including around 350,000 business premises.
For many organisations, migrating office telephony is no longer the hardest part.
The greater risk is the analogue service nobody realised was still connected.
Lift emergency phones, alarms, payment terminals, door entry systems and building equipment can all depend on PSTN lines. Openreach specifically warns businesses to identify this type of connected equipment before the deadline.
The priority is therefore not simply replace the phone lines.
It is: Find every dependency, understand how critical it is and decide whether to migrate, replace or protect it before the old network disappears.
When Is The UK PSTN Switch-Off?
The current deadline is 31 January 2027.
Openreach states that traditional business phone lines need to move to a digital service by that date. Businesses still using ISDN must also migrate the services supported by those lines to an IP-based alternative or risk the service being ceased.
This replaces earlier switch-off dates that appeared in older versions of this article.
Organisations should now work to the January 2027 deadline rather than relying on previous extensions.
What Is Actually Being Switched Off?
The PSTN is the ageing analogue telephone network that has historically carried traditional telephone services across the UK.
ISDN services also depend on that infrastructure.
Openreach says the network is increasingly difficult to maintain and no longer meets modern requirements, which is why services are moving towards digital alternatives.
For enterprise voice, this usually means moving towards technologies such as:
- SIP
- VoIP
- Microsoft Teams calling
- Cloud or hosted telephony
- Private cloud communications
- Hybrid communications
The important point is that the switch-off affects considerably more than employees making and receiving calls.
Which Business Services Could Still Depend On The PSTN?
This is where migration programmes can become complicated.
A business may have already moved its main telephone system to Teams, Mitel, Zoom or another digital platform while dozens of analogue lines remain elsewhere across its estate.
These can support:
- Lift emergency phones
- Fire and security alarms
- Payment terminals
- Door entry systems
- CCTV
- Building management systems
- Remote monitoring
- Fax
- Intercoms
- Emergency lines
- Specialist operational equipment
Openreach continues to highlight alarms, payment terminals, lift systems and other operational technology as areas businesses need to check.
These services are particularly easy to miss because responsibility may sit with facilities, security, finance or property teams rather than IT.
Why Is PSTN Migration Now A Business Continuity Issue?
A missed telephone line is inconvenient.
A failed lift emergency line, alarm or payment system can create a much more serious operational problem.
This changes the nature of the migration.
IT teams need to work with:
- Facilities
- Property
- Security
- Finance
- Operations
- Customer service
- Suppliers
- Landlords
- Building management teams
The objective is to identify every service that relies on the legacy network before it becomes unavailable.
Openreach has warned that businesses often have more devices connected to telephone lines than households, meaning migrations can take longer because equipment needs to be identified, tested and potentially replaced.
What Should Replace Existing PSTN Services?
There is no single migration path for every service.
The appropriate solution depends on what the line does.
| Existing Service | Potential Migration Approach |
| Enterprise voice | SIP, VoIP, Teams Direct Routing or another IP communications service |
| Existing PBX |
|
| Lift or emergency line | Compatible digital replacement or managed continuity where appropriate |
| Alarm or monitoring service | Confirm IP or mobile compatibility with the equipment provider |
| Payment terminal | Migrate to compatible IP or mobile connectivity |
| Fax | Cloud fax or digital workflow |
| Legacy operational equiptment | Assess replacement, alternative connectivity or transitional continuity |
The important step is not assuming that a solution suitable for telephony will automatically support every analogue device.
Equipment should be tested against its intended replacement before the existing service is ceased.
How Can Businesses Migrate Enterprise Voice?
For enterprise telephony, SIP provides a practical replacement for traditional PSTN and ISDN services.
Britannic's NetX is a carrier-grade SIP platform that can connect communications environments including Microsoft Teams, Zoom, Mitel, Avaya and Cisco while providing routing, number management, reporting and disaster recovery.
NetX is backed by a 99.999% SLA and allows organisations to retain greater control over routing and business continuity through the NetX portal.
This means PSTN migration does not necessarily require replacing the entire communications environment.
An organisation may be able to retain an existing PBX or contact centre while moving the underlying connectivity to SIP.
Can Microsoft Teams Replace PSTN Calling?
Microsoft Teams can become an enterprise voice platform when connected to external calling.
Britannic's NetX Direct Routing connects Microsoft Teams to the PSTN through the NetX SIP platform, allowing organisations to use Teams for external calls while retaining existing numbers and integrating with other communications environments.
For organisations already using Microsoft 365 extensively, PSTN migration can therefore become an opportunity to consolidate communications around Teams.
That decision should still be based on wider requirements such as contact centres, emergency calling, resilience, call recording and existing telephony investments.
What Happens If A Legacy Service Cannot Be Migrated In Time?
This is where Britannic's PSTN Assure proposition becomes particularly relevant.
Some organisations still have critical operational equipment that cannot realistically be replaced before the switch-off.
Britannic PSTN Assure is a managed continuity service designed to support compatible PSTN-dependent services such as:
- Lift emergency phones
- Alarm systems
- Payment terminals
- Door entry
- Building management systems
- Other operational infrastructure
It uses Metallic Path Facility, or MPF, to maintain the copper connectivity required by supported services without requiring an immediate migration to VoIP.
This creates additional time for organisations to assess and modernise legacy infrastructure in a controlled way.
PSTN Assure should therefore be treated as a continuity pathway, rather than an excuse to avoid long-term modernisation.
Why Should Businesses Not Rely On Emergency Voice Access?
Openreach has introduced Emergency Voice and Access Continuity, known as EVAc, as a temporary measure for some services that have not migrated by the deadline.
However, Openreach describes EVAc as a limited temporary voice-only service and warns that it may not support features businesses currently use. Organisations may also lose services altogether where an appropriate migration has not taken place.
EVAc should therefore not be treated as a migration strategy.
Businesses should have their intended operating model in place before January 2027.
What Changes When Voice Becomes Digital?
Moving from traditional PSTN lines to IP communications introduces different dependencies.
Traditional analogue telephones could often continue working during a local power failure because power was provided through the telephone network.
Digital services generally depend on:
- Local power
- Broadband or network connectivity
- Routers and network equipment
- Cloud or hosted platforms
- SIP connectivity
Openreach specifically warns that digital phone lines may not work during a power cut unless appropriate backup arrangements are available.
Businesses therefore need to test resilience rather than assuming a digital replacement behaves exactly like the analogue service it replaced.
How Can Businesses Make Digital Communications More Resilient?
Moving to IP creates opportunities to design stronger resilience.
For example, NetX can automatically reroute calls if a primary destination becomes unavailable, supporting disaster recovery without relying on employees physically accessing a telephone system.
Connectivity should also be considered.
Britannic's Unlimited Cellular Backup provides an independent mobile connection alongside broadband, fibre or Ethernet. If the fixed connection becomes unavailable, traffic can automatically move to the cellular path and return once the main connection recovers.
This can help protect services including:
- IP telephony
- Cloud applications
- Payment systems
- Internet access
- Customer service platforms
Power resilience should be assessed separately through appropriate UPS or power-continuity arrangements.
A resilient digital communications environment should avoid replacing one legacy dependency with a new single point of failure.
The Britannic PSTN Migration Framework
Britannic recommends approaching the remaining migration through five stages.
Find
Identify every PSTN and ISDN line across the estate.
Do not limit the audit to telephony.
Classify
Establish what each line supports and how critical that service is.
A rarely used fax line should not carry the same priority as an emergency lift phone.
Decide
Choose whether the service should be:
Migrated → Replaced → Protected → Retired
Not every legacy service needs a like-for-like replacement.
Test
Confirm the replacement works under real operating conditions.
Test calling, alarms, payments, emergency functions, network failure and other relevant scenarios before disconnecting the existing line.
Protect
Build appropriate continuity around services that have become dependent on IP connectivity.
Find → Classify → Decide → Test → Protect
The most dangerous PSTN line is often not the obvious one.
It is the line nobody knew was still important.
What Should A PSTN Audit Include?
Organisations approaching the final months before switch-off should check:
- All active PSTN and ISDN numbers
- Main office telephone systems
- Contact centres
- SIP migration requirements
- Microsoft Teams calling
- Lift emergency phones
- Fire and intruder alarms
- Payment terminals
- Door entry
- CCTV
- Fax
- Building management systems
- Remote monitoring
- Telephone lines without obvious users
- Services managed by facilities or property teams
- Third-party supplier contracts
- Multi-site estates
- Power requirements
- Network resilience
- Mobile coverage
- Failover
- Business continuity plans
- Testing and acceptance processes
Every remaining line should have a named owner and an agreed outcome.
Why Should Multi-Site Organisations Act Quickly?
Complexity increases significantly across large estates.
A single organisation may have hundreds of telephone numbers spread across offices, branches, housing stock, campuses, clinics or operational sites.
Some may have been installed many years ago with limited documentation.
Openreach warned in April 2026 that around 3,000 commercial buildings in London alone still had at least one premises using the legacy PSTN, potentially placing phone, alarm, monitoring and backup services at risk.
Finding these dependencies can therefore take considerably longer than ordering their replacement.
Organisations with large property estates should prioritise discovery immediately.
The PSTN Switch-Off Can Also Be An Opportunity
Migration is necessary, but it does not have to be treated purely as a compliance exercise.
Replacing traditional voice connectivity can create opportunities for:
- Flexible call routing
- Better disaster recovery
- Number management
- Microsoft Teams integration
- Cloud and hybrid communications
- Improved reporting
- Fraud monitoring
- Remote working
- Centralised administration
- Greater visibility of call performance
NetX, for example, can provide advanced routing, analytics, fraud monitoring and integrations alongside the SIP connectivity replacing legacy telephony.
The best PSTN migration therefore solves the immediate deadline while improving the communications environment that remains afterwards.
The Deadline Is Close, But Migration Should Still Be Controlled
With the switch-off scheduled for 31 January 2027, organisations no longer have time for an open-ended review.
That does not mean every remaining analogue service should be replaced in a rush.
The priority should be to understand the estate and choose an appropriate path for each dependency.
Enterprise voice can move to SIP, Direct Routing or another digital communications platform.
Obsolete services can be retired.
Legacy equipment can be replaced where practical.
Critical services that cannot yet move may have a transitional option through PSTN Assure.
Britannic combines NetX SIP, Direct Routing, PSTN Assure, connectivity resilience and managed services to help organisations manage both the immediate switch-off and the longer-term communications environment.
Organisations with remaining PSTN or ISDN services can book a complimentary meeting with Britannic to identify outstanding dependencies, prioritise critical services and create a migration or continuity plan before January 2027.
