PSTN Switch-Off 2027: What Every UK Business Must Do Before the Deadline

The UK’s traditional telephone network is approaching the end of its life.

On 31 January 2027, BT plans to retire the Public Switched Telephone Network, commonly known as the PSTN. Businesses still using traditional telephone lines, ISDN services or equipment connected to an analogue line will need to move to a digital alternative before the deadline. 

For many organisations, the change will involve moving their telephone system to Voice over Internet Protocol, or VoIP.

However, the PSTN switch-off is not only about office telephones.

Analogue lines are frequently hidden inside alarm systems, lift emergency phones, payment terminals, fax machines, door-entry systems and monitoring equipment. Businesses that only review their main telephone system could therefore overlook essential services that may stop working after the switch-off.

With the deadline now close, every UK business should identify what still relies on the old network, decide how it will be replaced and test the new arrangements before January 2027.

What Is the PSTN?

The Public Switched Telephone Network is the traditional infrastructure that has delivered landline telephone services across the UK for decades.

It was designed primarily for voice calls, using physical telephone lines and telephone exchanges. The network has also supported services such as:

• Analogue telephone lines
• ISDN telephone systems
• ADSL broadband
• Alarm signalling
• Fax machines
• Payment terminals
• Remote monitoring equipment
• Lift emergency telephones

The technology is now ageing, increasingly difficult to maintain and no longer suited to modern communications.

Government guidance states that replacement parts are no longer being manufactured and that maintaining the PSTN increasingly depends on reusing components recovered from decommissioned areas of the network. The same guidance reports that PSTN incidents increased by 45% during 2024, with more than 2,600 major incidents recorded during 2024/25. 

The move to digital services is therefore not simply an optional technology upgrade. It is the replacement of an ageing national network that is reaching the end of its serviceable life.

When Is the PSTN Switch-Off?

BT intends to retire the PSTN by 31 January 2027.

Other telecommunications providers that use BT’s underlying network must work to the same timescale, while providers operating their own networks are following broadly similar migration plans. 

The original target was December 2025, but the timetable was extended to allow more time for complex migrations, including services supporting vulnerable people and critical infrastructure.

Businesses should not interpret the extension as a reason to delay.

Providers are already withdrawing older products, migrating customers and placing restrictions on the sale or modification of traditional services. Some services cannot be migrated automatically and may stop working if the customer has not arranged a suitable replacement before the deadline. 

Is the PSTN Switch-Off the Same as the Copper Switch-Off?

Not exactly.

The PSTN switch-off refers primarily to the retirement of the traditional telephone switching network and the services that depend on it.

The wider replacement of copper cabling with full-fibre infrastructure is a related but separate programme. Copper connections will not necessarily disappear from every location on 31 January 2027.

However, businesses using copper-based telephone or broadband products may still need to change service.

For example, an organisation may move from traditional ADSL broadband to full fibre, or from an analogue telephone line to a digital service delivered through its router.

The important question is not simply whether a copper cable enters your building. It is whether any of your services still depend on a legacy PSTN, ISDN or Wholesale Line Rental product.

Which Business Services Could Be Affected?

The most obvious affected service is the office telephone system.

Businesses using analogue telephone lines, ISDN2 or ISDN30 may need to move to a hosted VoIP platform, SIP service or another modern communications solution.

However, many businesses have additional devices connected to telephone sockets that are easily forgotten.

Government and industry guidance specifically identifies analogue phones, alarms, payment terminals, lifts, intercom systems and broadband services as systems that may require replacement or reconfiguration. 

Telephone Systems

Older telephone systems may use analogue lines or ISDN circuits.

Some existing telephone hardware can be adapted, but in many cases it will make more sense to replace the system with a cloud-based VoIP platform.

Modern systems can provide:

• Mobile and desktop calling applications
• Call queues
• Auto-attendants
• Call recording
• Voicemail-to-email
• Remote-working support
• Reporting and analytics
• Microsoft Teams integration
• CRM integration

Businesses should review whether their existing handsets, cabling and telephone numbers can be retained.

Intruder and Fire Alarms

Many older alarm systems use an analogue telephone line to report an incident to an alarm receiving centre.

The alarm may continue to appear operational locally even when its external signalling no longer works. This creates a serious risk because the business may not realise that alerts are failing to reach the monitoring provider.

Speak directly to the alarm maintenance company and ask whether the signalling equipment is suitable for an all-IP network.

Depending on the system, it may need to be replaced with an IP, mobile or dual-path signalling solution.

Lift Emergency Telephones

Lift emergency phones are particularly important because they may be required to work when somebody is trapped inside the lift.

Older lift phones commonly rely on analogue telephone lines. Digital alternatives may require a network connection, mobile connectivity and appropriate battery backup.

The lift maintenance provider should confirm:

• Whether the current equipment is PSTN-dependent
• What replacement equipment is required
• How calls will be routed
• How the system will operate during a power failure
• How the replacement will be tested

Do not assume that the telecommunications provider will automatically upgrade equipment installed inside the lift.

Door-Entry and Intercom Systems

Some door-entry systems dial a landline or mobile number when a visitor presses a button.

Older installations may contain an analogue dialler that will not operate correctly over a digital service.

Your access-control provider should verify compatibility and recommend an IP or mobile-based replacement where required.

Payment Terminals and EPOS Systems

Modern payment terminals normally use broadband or mobile connectivity, but older terminals may still dial over an analogue line.

Retailers, hospitality businesses and organisations processing payments should confirm the connection method used by every terminal.

Losing telephone service is inconvenient. Losing the ability to accept payments can stop the business from trading.

Fax Machines

Traditional fax machines were designed to communicate across analogue telephone networks.

Fax transmission over VoIP can be unreliable because the technologies used to compress and manage voice traffic do not always handle fax signals correctly.

Businesses that still depend on fax should consider moving to:

• Secure email
• Digital document portals
• Electronic signatures
• Cloud fax services
• Sector-specific secure messaging platforms

Any replacement must be suitable for the sensitivity of the information being transmitted.

CCTV and Monitoring Equipment

Older CCTV, telemetry and remote-monitoring systems may use analogue diallers or modems.

This can include equipment for:

• Refrigeration monitoring
• Environmental sensors
• Building-management systems
• Remote access
• Water or energy monitoring
• Lone-worker systems
• Plant and machinery alerts

Ofcom has warned that non-voice equipment such as alarms, telemetry and monitoring systems may need to be reconfigured or replaced because certain PSTN characteristics, including line powering, may not be reproduced by an all-IP service. 

What Happens If a Business Does Nothing?

Businesses should not assume that their provider will automatically convert every service.

Some basic telephone lines may be moved through a provider-led migration programme. However, more complicated services, including certain ISDN, multiline and specialist services, cannot necessarily be migrated automatically.

BT states that services unable to be moved through its protective migration programme could stop working from 31 January 2027. Connected equipment such as alarms, lifts and CCTV may also stop working or be left with only limited functionality. 

Potential consequences include:

• Telephone numbers becoming unavailable
• Customers being unable to contact the business
• Emergency or alarm calls failing
• Payment terminals losing connectivity
• Lift emergency phones becoming unusable
• Fax services stopping
• Broadband disruption
• Unplanned replacement costs
• Emergency installation charges
• Business downtime

Waiting until the final weeks also reduces the time available for number porting, engineering work, supplier coordination and testing.

Moving to VoIP

Voice over Internet Protocol carries telephone calls over an IP network rather than the traditional PSTN.

For users, making and receiving calls may feel much the same. The main difference is that the telephone service now depends on the business’s internet connection, local network and electrical supply.

VoIP can be delivered through:

• Physical IP desk phones
• Applications on computers
• Mobile applications
• Microsoft Teams
• Browser-based calling
• Existing systems connected through suitable gateways
• Hosted telephone platforms

A properly designed VoIP system can give a business considerably more flexibility than a traditional telephone line.

Employees can use their business number from different locations, calls can be redirected between sites and capacity can be increased without installing additional physical lines.

BT identifies features including call forwarding, call recording, virtual meetings, instant messaging and integration with collaboration platforms as potential benefits of moving to IP communications. 

Digital Phones Depend on Power and Connectivity

Traditional corded telephones could sometimes continue working during a local power cut because they received power through the telephone line.

Digital telephone services normally rely on equipment such as:

• The broadband router
• The fibre optical network terminal
• Network switches
• Wi-Fi access points
• Telephone handsets
• The hosted telephone provider
• The internet connection

If these devices lose power or connectivity, the telephone service may stop working.

Ofcom advises that a digital telephone will only operate during a power cut where suitable battery backup is available. Providers are required to offer an emergency-calling solution to customers who depend entirely on their landline, but businesses should assess their wider operational requirements rather than assuming basic provider protection will be sufficient. 

A business resilience plan may include:

• Uninterruptible power supplies
• Battery-backed network equipment
• Secondary internet connectivity
• 4G or 5G failover
• Mobile calling applications
• Call forwarding during outages
• Diverse connectivity for important sites
• Documented emergency numbers

The correct solution depends on how critical telephone availability is to the organisation.

A professional-services business may tolerate a short interruption by diverting calls to mobiles. A care provider, medical organisation, call centre or emergency service may require a much higher level of resilience.

Can You Keep Your Existing Telephone Numbers?

In many cases, existing telephone numbers can be transferred to the new service.

However, number porting must be planned carefully.

Before changing provider or cancelling an old telephone service, confirm:

• Which numbers belong to the business
• Which numbers are actively published
• Whether each number can be ported
• Who legally owns the numbers
• Whether any numbers are attached to secondary lines
• How long the porting process is expected to take
• What happens to calls during migration
• Whether fax or alarm numbers are also being used

Do not cancel the old service before the number transfer has been completed. Cancelling too early could result in the number being lost.

Businesses should also test incoming and outgoing calls after migration, including calls to mobile numbers, international destinations and emergency services where appropriate.

What Every UK Business Should Do Before 2027

1. Audit Every Telephone Line

Start with invoices from telephone and internet providers.

Identify every PSTN, ISDN, analogue, WLR and ADSL service for every business location.

Do not assume an unfamiliar line is unused simply because nobody recognises the telephone number. It may support an alarm, lift or monitoring device.

2. Physically Inspect the Premises

Look for equipment connected to telephone sockets.

Check:

• Communications cupboards
• Reception areas
• Alarm panels
• Lift control rooms
• Server rooms
• Plant rooms
• Payment areas
• Entry systems
• Remote buildings
• Warehouses
• Home-worker installations

Label each line and record what it supports.

3. Speak to Every Relevant Supplier

Your telephone provider may not be responsible for your alarm, lift, access-control or payment equipment.

Contact each equipment provider separately and ask for written confirmation of compatibility.

Ask whether the equipment:

• Works over VoIP
• Requires an analogue telephone adapter
• Should be reconfigured
• Needs to be replaced
• Requires battery backup
• Can use mobile connectivity
• Must be tested with a monitoring centre

4. Choose a Replacement Telephone System

Review how the business currently handles calls and what it will require over the next few years.

Consider:

• Number of users
• Multiple locations
• Remote and hybrid working
• Call recording
• Call queues
• Reporting
• Customer-service requirements
• Microsoft Teams integration
• Mobile applications
• Business continuity
• Compliance obligations

The objective should not be to reproduce an outdated telephone system exactly. The migration is an opportunity to improve how calls are handled.

5. Review the Internet Connection

VoIP performance depends on reliable connectivity.

Check whether the business has:

• Adequate bandwidth
• Stable broadband
• Suitable network equipment
• Correct traffic prioritisation
• Reliable Wi-Fi
• Appropriate firewall configuration
• Backup connectivity

Poor local networks can cause dropped calls, delays or one-way audio even when the VoIP platform itself is functioning correctly.

6. Plan Power and Internet Resilience

Decide how employees will communicate if the internet or electrical supply fails.

Important sites may require UPS protection, secondary broadband and automatic mobile failover.

Document how calls will be redirected and make sure employees understand the procedure.

7. Protect the New Telephone System

Moving telephone services online introduces different security considerations.

VoIP systems should be protected with:

• Strong administrator passwords
• Multi-factor authentication
• Restricted administrative access
• Secure device configuration
• Call-spend controls
• International-dialling restrictions
• Monitoring and alerting
• Prompt security updates
• Regular account reviews

A compromised telephone account can be used for fraudulent calling, impersonation or access to recorded conversations.

8. Arrange Migration Early

Engineering availability and supplier capacity are likely to come under pressure as the deadline approaches.

Businesses with several premises, specialist equipment or complex number ranges should begin immediately.

Allow time for unexpected complications rather than planning to finish on 30 January 2027.

9. Test Everything

A migration is not complete when the new equipment has simply been switched on.

Test:

• Incoming calls
• Outgoing calls
• Main published numbers
• Call queues
• Voicemail
• Call recording
• Out-of-hours routing
• Alarm signalling
• Lift emergency calls
• Door entry
• Payment terminals
• Failover connections
• Operation during a simulated power failure

Record the results and ask the relevant supplier to confirm that monitored devices have communicated successfully.

10. Update Your Documentation

Create an accurate record containing:

• Telephone numbers
• Service providers
• Contract details
• Number-porting information
• Device locations
• Alarm and lift suppliers
• Emergency contacts
• Network dependencies
• Power-backup arrangements
• Renewal dates
• Support procedures

This will make future troubleshooting and supplier management considerably easier.

Do Not Wait for the Deadline

The PSTN switch-off is a significant national infrastructure change, but it does not need to cause disruption.

The businesses most at risk are not necessarily those with the largest or most complicated telephone systems. They are the businesses that do not know which services depend on their existing lines.

An old telephone socket in a cupboard may appear insignificant until it becomes clear that it connects a fire alarm, lift phone or payment terminal.

The first step is therefore visibility.

Find every line, identify every connected service and speak to the companies responsible for maintaining them.

Once that work has been completed, the migration can be planned properly rather than handled as an emergency.

How Hamilton Group Can Help

Hamilton Group can help your business prepare for the PSTN and ISDN switch-off before the 31 January 2027 deadline.

We can review your existing communications, identify legacy services and help you move to a modern digital solution with minimal disruption.

Our support can include:

• PSTN and ISDN line audits
• Hosted VoIP telephone systems
• Microsoft Teams calling
• Telephone-number porting
• Full-fibre and business-connectivity upgrades
• 4G and 5G internet failover
• Firewall and network configuration
• Power-resilience planning
• Supplier coordination
• Multi-site migrations
• Call-flow design
• Security reviews
• Post-migration testing
• Ongoing IT and communications support

At Hamilton Group, we aim to make first contact on IT support requests within 15 minutes, helping your employees receive assistance quickly when an IT or communications problem affects the business.

Do not leave your migration until the final weeks of the switch-off programme.

Call Hamilton Group on 0330 043 0069 to arrange a review of your telephone lines, connected equipment and digital communications requirements.