Replace your traditional phone lines before 31 January 2027
The UK's traditional telephone network is being retired.
BT Group plans to switch off the Public Switched Telephone Network, known as the PSTN, by 31 January 2027. Businesses still using affected analogue, ISDN or copper-based services need to move to suitable digital alternatives before that date.
Replacing the main office telephone system may be the obvious part.
The greater risk is often the line nobody remembers.
It may connect:
- A lift emergency telephone
- A security or fire alarm
- A door-entry system
- A fax machine
- A payment terminal
- CCTV equipment
- A boiler or plant-room alarm
- An intercom
- A remote monitoring system
- An older broadband service
These services may have been installed many years ago. They may be managed by different departments, maintained by external contractors or billed under descriptions nobody recognises.
If they are not identified and migrated, they could stop working when the underlying legacy service is withdrawn.
Stratiis can help you identify your affected lines, understand what is connected and create a controlled migration plan.
Find every legacy service. Replace it safely. Avoid a last-minute emergency.
What is the PSTN switch-off?
PSTN stands for Public Switched Telephone Network.
It is the traditional network that has carried landline telephone calls and supported related analogue services across the UK.
This older network is being replaced by modern digital services using Internet Protocol technology.
In future, most fixed business calls will be carried digitally through services such as Voice over Internet Protocol, commonly called VoIP. Ofcom explains that digital landline services use a broadband connection rather than the traditional analogue telephone network.
You may also hear the change described as:
- The analogue switch-off
- The landline switch-off
- The ISDN switch-off
- The digital switchover
- The move to All-IP
- The copper switch-off
- The move to digital phone lines
These terms are often used together, although they can refer to different parts of the wider change.
For your business, the most important question is:
Which of your services still depend on the old network?
When is the PSTN switch-off?
The current deadline for BT Group's PSTN retirement is 31 January 2027. Openreach and BT Business both advise organisations using traditional services to move to digital alternatives before that date.
Some communications providers may set earlier migration dates for their own customers.
Openreach has warned that some providers are working towards dates earlier than the final national deadline.
This means 31 January 2027 should not be treated as the day to start your project.
It is the date by which the migration should already be complete.
Businesses with several sites, complex number ranges, older phone systems or connected building equipment should begin planning as early as possible.
Why is the PSTN being switched off?
The traditional network was built for an earlier generation of telephone services.
It is becoming increasingly difficult to maintain, while businesses now depend heavily on cloud applications, mobile working, digital communications and internet-based systems.
The change allows telephone services to move onto modern IP-based infrastructure.
For businesses, that can provide opportunities to introduce:
- Hosted Voice
- Microsoft Teams Phone
- Unified Communications
- More flexible call routing
- Mobile and desktop calling
- Easier hybrid working
- Improved reporting
- Multi-site communications
- Better business-continuity options
- Integration with customer systems
However, the opportunity to modernise should not distract from the immediate risk.
Every legacy line and connected service needs to be identified before it is withdrawn.
Will ordinary business landlines stop working?
Traditional analogue services will need to be moved to digital alternatives.
That does not mean your business must lose its landline numbers.
In many cases, you can retain established geographic telephone numbers by transferring them to:
- Hosted Voice
- Microsoft Teams Phone
- SIP Trunking
- A digital phone-line service
- Another supported cloud telephone platform
The telephone number may remain the same.
What changes is the technology carrying the call.
The migration still needs to be planned carefully, particularly where numbers are linked to broadband services, direct-dial ranges or several sites.
Is your business ready?
You may not be ready for the switch-off if:
- You still pay for analogue telephone lines
- Your phone system uses ISDN
- You have unidentified numbers on telephone bills
- Nobody knows which lines support alarms or lifts
- Your fax machine still uses a wall socket
- Your broadband is tied to an older phone line
- You have several offices using different providers
- Your existing phone system is no longer supported
- You have no plan for power or internet outages
- Your business numbers have not been checked
- Nobody has spoken to your alarm, lift or door-entry suppliers
- You are waiting for your provider to contact you
A provider may know which services it bills.
It may not know what third-party equipment your organisation has connected to those services.
Your business needs its own complete inventory.
What services could be affected?
Analogue telephone lines
Traditional analogue lines may be used for:
- Individual desk phones
- Reception numbers
- Fax machines
- Alarms
- Lifts
- Door entry
- Payment devices
- Emergency phones
- Remote monitoring
Each line should be traced before it is cancelled.
A line that appears unused may still support important equipment.
ISDN telephone services
ISDN has commonly been used to connect business telephone systems to the public telephone network.
Affected organisations may need to move to:
- SIP Trunking
- Hosted Voice
- Microsoft Teams Phone
- Another digital telephone service
The right answer depends on whether the existing telephone system remains supported and suitable.
Traditional business phone systems
Older telephone systems may rely on ISDN or analogue services for external calls.
Possible options include:
- Retaining the system and adding SIP Trunks
- Upgrading the system
- Replacing it with Hosted Voice
- Moving users to Microsoft Teams Phone
- Introducing a phased migration
A technical assessment should confirm whether the system:
- Supports SIP
- Remains under manufacturer support
- Can receive security updates
- Supports your current call flows
- Can support remote working
- Is worth maintaining
Copper-based broadband
Some older broadband services share infrastructure with legacy phone products.
Openreach states that copper broadband and business phone services are affected by the January 2027 transition. It also identifies FTTC services as part of the wider move away from copper-based products.
Your replacement may involve:
- Full Fibre
- SoGEA
- Business broadband
- A leased line
- Mobile connectivity
- Another managed data service
Full Fibre operates using fibre infrastructure rather than relying on the PSTN in the same way.
Do not cancel an old telephone line until you have confirmed whether broadband depends on it.
Equipment that businesses often overlook
Alarm systems
Security, fire or environmental alarms may use an analogue line to communicate with a monitoring centre.
Speak to the alarm maintenance company and confirm:
- How the alarm currently communicates
- Whether it supports IP or mobile connectivity
- Whether replacement equipment is required
- Whether backup communication is included
- What happens during a power cut
- How the new connection will be tested
- Whether certification or maintenance terms are affected
Do not assume that connecting an alarm to a standard analogue adapter will provide a supported replacement.
Lift emergency telephones
Lift emergency phones may rely on traditional telephone lines.
The replacement must allow a person trapped in the lift to contact the appropriate support service reliably.
Your audit should identify:
- Every lift
- Every telephone line
- The lift-maintenance provider
- The emergency call destination
- The proposed replacement technology
- Battery backup
- Mobile signal where applicable
- Testing and sign-off requirements
BT specifically identifies lift lines among the services businesses need to review before the PSTN retirement.
Door-entry and intercom systems
Door-entry systems may use analogue lines to call:
- Reception
- A concierge
- A tenant
- A mobile number
- A monitoring service
The replacement may involve:
- An IP module
- Mobile connectivity
- A new intercom platform
- Replacement hardware
- Integration with an access-control system
The equipment manufacturer or maintenance company should confirm compatibility.
Fax machines
Traditional fax machines may not operate reliably over every digital voice service.
Consider whether the process can move to:
- Secure email
- Digital fax
- Customer portals
- Secure file sharing
- Electronic signatures
- A line-of-business application
Where fax must remain, test sending and receiving with the organisations you communicate with regularly.
Payment terminals
Payment terminals may connect using analogue, broadband or mobile services.
Confirm with the payment provider:
- How the device connects
- Whether replacement hardware is required
- Whether it supports the new network
- Whether firewall changes are needed
- What happens if the internet fails
- Whether mobile backup is available
A payment device should not be moved to an untested connection without supplier approval.
CCTV and remote monitoring
Older CCTV systems may use telephone lines for:
- Remote access
- Fault alerts
- Alarm signalling
- Monitoring-centre communication
The system may need:
- Fixed broadband
- Mobile data
- A private network
- Replacement recording equipment
- New cameras or communication modules
Security and data usage should be considered as part of the replacement.
Building-management equipment
Legacy telephone connections may exist in:
- Boiler rooms
- Plant rooms
- Heating systems
- Environmental monitors
- Energy systems
- Pumps
- Water systems
- Remote maintenance equipment
These services may be controlled by facilities or property teams rather than IT.
A complete PSTN project needs participation from every relevant department.
Emergency and refuge telephones
Emergency phones may exist in:
- Car parks
- Stairwells
- Refuge areas
- Remote sites
- Communal buildings
- Supported accommodation
- Security locations
- Warehouses
Because these devices may be used rarely, they can easily be overlooked.
They should be identified, prioritised and tested carefully.
Why your telephone bill is not enough
A telephone invoice may show:
- A telephone number
- A line charge
- A circuit reference
- An unfamiliar product name
- An old account name
- A general site address
It may not explain what is connected.
The equipment may be:
- Hidden in a plant room
- Installed in a lift
- Inside a communications cabinet
- Managed by an external contractor
- Paid for through another department
- Labelled incorrectly
- Missing from the asset register
Calling the number may not help.
The line may connect silently to equipment or appear unused until an emergency occurs.
A proper audit combines billing information with physical checks and supplier records.
What should a PSTN switch-off audit include?
A useful audit should record:
- Telephone number
- Provider
- Account number
- Circuit reference
- Site address
- Exact physical location
- Service type
- Connected equipment
- Internal owner
- Maintenance supplier
- Business importance
- Contract end date
- Replacement plan
- Power requirements
- Connectivity requirements
- Test method
- Migration status
- Cancellation approval
The goal is not simply to produce a list.
It is to create a working migration plan for every affected service.
A simple PSTN migration register
| Existing service | Location | Connected equipment | Proposed replacement | Owner | Status |
|---|---|---|---|---|---|
| ISDN service | Glasgow office | Business phone system | SIP Trunks | IT | Assessment |
| Analogue line | Lift room | Emergency lift phone | Mobile communicator | Facilities | Supplier booked |
| Analogue line | Reception | Door-entry system | IP module | Property | Testing |
| Copper broadband | Branch office | Router and office network | Full Fibre | IT | Ordered |
| Analogue line | Finance office | Fax machine | Digital fax | Finance | Approved |
| Analogue line | Plant room | Boiler alarm | IP monitoring | Facilities | Investigation |
Your register should also include dates, costs, risks and testing evidence.
What should replace your traditional telephone system?
Hosted Voice
Hosted Voice moves the main telephone platform into the cloud.
It may provide:
- Existing number migration
- Desk phones
- Desktop applications
- Mobile applications
- Auto-attendants
- Call queues
- Voicemail
- Call reporting
- Call recording
- Hybrid-working support
- Multi-site calling
Hosted Voice may be appropriate where the existing telephone system is ageing or no longer supports the way employees work.
Microsoft Teams Phone
Microsoft Teams Phone allows users to make and receive external business calls through Microsoft Teams.
It may provide:
- Existing business numbers
- External calling
- Auto-attendants
- Call queues
- Voicemail
- Desktop and mobile access
- Teams-certified phones
- Microsoft 365 integration
- Hybrid-working support
It can be a strong option where Teams is already central to the organisation.
Reception, contact centre and common-area requirements should still be reviewed carefully.
SIP Trunking
SIP Trunking can connect a compatible existing telephone system to a modern IP-based voice service.
It may be suitable when:
- The existing phone system remains supported
- The hardware is reliable
- Employees know how to use it
- Replacing the whole platform is not yet justified
- A phased migration is preferred
SIP may not offer good value if the telephone system is already near the end of its useful life.
Digital phone lines
Some low-volume or simple services may be replaced by a digital phone-line product rather than a complete cloud telephone platform.
This may suit:
- A simple office number
- A small site
- A low-use handset
- A limited temporary requirement
Connected equipment still needs to be checked for compatibility.
Mobile connectivity
Some devices may move to:
- 4G
- 5G
- Data-only SIMs
- Multi-network SIMs
- Mobile routers
- Specialist mobile communicators
This can be useful for alarms, monitoring equipment, temporary sites and internet failover.
Coverage and power arrangements must be tested at the actual location.
Can you keep your existing telephone numbers?
In many cases, yes.
Number porting allows established numbers to be transferred to a new communications provider.
Before porting, confirm:
- The legal account name
- Installation address
- Billing address
- Current provider
- Main billing number
- Complete number range
- Direct-dial numbers
- Linked broadband
- Connected services
- Required migration date
Do not cancel the existing service before the number has transferred.
A premature cancellation can cause disruption and may make the number more difficult to recover.
Power cuts and digital phone services
Traditional analogue lines could often continue working during a local power failure because power was supplied through the telephone network.
Digital services normally depend on powered equipment such as:
- Routers
- Firewalls
- Network switches
- Optical network terminals
- IP phones
- Telephone systems
- Session Border Controllers
- Analogue adapters
Ofcom highlights that digital telephone services depend on mains electricity and may not operate during a power cut without backup arrangements.
Business continuity options may include:
- Uninterruptible Power Supplies
- Battery backup
- Generators
- Mobile applications
- Mobile phones
- Alternative call routing
- Secondary sites
- Emergency communication procedures
The required level of protection should match the importance of the service.
Internet outages and digital calling
Cloud phone systems depend on internet or data connectivity.
You should understand:
- What happens when the main connection fails
- Whether calls automatically route elsewhere
- Whether users can work from another location
- Whether a mobile application remains available
- Whether backup connectivity activates automatically
- Whether critical devices have separate communication paths
- How long a provider fault may take to repair
Possible continuity measures include:
- A second fixed internet connection
- 4G or 5G failover
- A different network provider
- Provider-level call diversion
- Mobile applications
- Another office
- An external answering service
Backup services should be tested before the old lines are removed.
PSTN switch-off for different sectors
PSTN switch-off for housing associations
Housing associations may have a large number of affected services spread across:
- Head offices
- Local offices
- Housing developments
- Sheltered housing
- Supported accommodation
- Community facilities
- Concierge stations
- Lifts
- Door-entry systems
- Alarm systems
- CCTV
- Plant rooms
- Emergency phones
The programme may involve:
- IT
- Property services
- Asset management
- Housing teams
- Repairs
- Compliance
- Finance
- External contractors
A central migration register is essential.
The organisation should give particular attention to:
- Vulnerable tenants
- Emergency communications
- Accessibility
- Power resilience
- Mobile coverage
- Contractor responsibilities
- Resident communication
- Testing evidence
PSTN switch-off for accountancy firms
An accountancy firm may need to review:
- Main office numbers
- Direct-dial ranges
- ISDN telephone systems
- Fax services
- Alarm lines
- Door entry
- Payment terminals
- Copper broadband
- Multi-office communications
The change also creates an opportunity to improve:
- Hybrid working
- Client call handling
- Multi-office reception
- Microsoft Teams use
- Business continuity
- Call reporting
PSTN switch-off for charities
Charities may work from a mixture of:
- Owned premises
- Rented offices
- Community buildings
- Shared facilities
- Temporary locations
Before replacing a service, confirm:
- Who owns the line
- Who owns the equipment
- Whether it is shared
- Whether the landlord is responsible
- Which maintenance supplier is involved
- Whether a vulnerable service user depends on it
- How the replacement will be funded
A charity should not automatically pay to replace a landlord-owned service without confirming responsibility.
PSTN switch-off for multi-site organisations
Multi-site businesses may have:
- Several communications providers
- Different billing accounts
- Different alarm suppliers
- Several phone systems
- Inconsistent site names
- Unknown legacy numbers
- Different broadband products
A standardised migration programme should include:
- One audit format
- One risk-rating approach
- Defined replacement standards
- Consistent testing
- Central supplier records
- Clear cancellation approval
- Regular progress reporting
This reduces the risk of a small or remote site being forgotten.
Common PSTN switch-off mistakes
Waiting for the final deadline
Connectivity installation, equipment replacement and number porting may take longer than expected.
Reviewing only the main phone system
Alarms, lifts, broadband and building equipment may create greater risk.
Assuming the provider knows everything
A telecoms provider may not know what third-party equipment is attached to a line.
Cancelling a line that appears unused
It may support broadband, an alarm or another hidden service.
Cancelling before number porting
This can interrupt calls and put established numbers at risk.
Assuming an adapter will solve everything
Some analogue equipment is not supported reliably over digital voice.
Ignoring power failure
Digital devices need local power.
Ignoring internet failure
Cloud calling requires suitable connectivity and failover planning.
Treating the project as an IT-only task
Facilities, finance, property, security and contractors may hold important information.
Failing to test the replacement
A new service is not complete until its real business function has been tested.
What happens if your business does nothing?
Services that remain dependent on withdrawn legacy products may stop working or may no longer be supported after the transition.
BT Business advises organisations using analogue networks to move to fully digital IP-based services before 31 January 2027 to protect continuity.
Possible consequences include:
- Loss of telephone service
- Missed customer calls
- Alarm communication failures
- Lift emergency-phone failures
- Door-entry problems
- Broadband disruption
- Payment-terminal failures
- Loss of remote monitoring
- Emergency communication risks
- Urgent replacement costs
- Business interruption
- Difficulty retaining established numbers
The most expensive migration is often the one completed urgently after something stops working.
The benefits of acting early
More time to find hidden lines
You can investigate unclear bills and inspect remote sites properly.
More supplier choice
You have time to compare platforms, contracts and replacement equipment.
Safer number migration
Account problems and rejected porting requests can be resolved before the deadline.
Better testing
New services can be tested before old services are cancelled.
Better resilience
Power and internet failover can be planned properly.
Less disruption
Migrations can be phased around business operations.
Lower unnecessary costs
Unused lines, numbers and services can be identified and removed.
A stronger communications strategy
The change can support hybrid working, cloud calling and improved customer service.
What should you look for in a PSTN migration partner?
A complete audit
The provider should look beyond the main telephone handsets.
Voice expertise
They should understand analogue lines, ISDN, SIP, Hosted Voice and Teams Phone.
Number-porting experience
They should understand single numbers, direct-dial ranges and linked services.
Connectivity knowledge
They should understand broadband, Full Fibre, leased lines and internet failover.
Third-party coordination
They should recognise when alarm, lift, payment or door-entry specialists must be involved.
Clear documentation
You should receive a service register, risk assessment, migration plan and test record.
Business-continuity planning
The provider should ask what happens during internet and power failures.
Controlled cancellation
Legacy services should not be ceased until dependencies have been checked.
Ongoing support
You need one clear support route when several suppliers are involved.
Our PSTN switch-off process
1
Discovery
We start by understanding:
- Your locations
- Current telephone systems
- Providers
- Broadband services
- Known analogue lines
- Number ranges
- Connected building equipment
- Internal owners
- External contractors
- Continuity requirements
2
Billing and service review
We review available:
- Telephone invoices
- Broadband invoices
- Circuit records
- Number lists
- Contracts
- Asset registers
- Supplier records
- Maintenance agreements
This forms the starting point for the migration register.
3
Site and equipment audit
Where appropriate, we help investigate:
- Communications cabinets
- Telephone sockets
- Routers
- Alarm panels
- Lift equipment
- Door-entry systems
- Fax machines
- Payment terminals
- Emergency phones
- Plant rooms
We record what is connected and identify the responsible owner or supplier.
4
Risk classification
Each service is assessed according to:
- Safety impact
- Customer impact
- Operational importance
- Financial importance
- Availability requirement
- Power dependency
- Connectivity dependency
- Replacement lead time
Critical services are prioritised.
5
Replacement planning
The migration plan may include:
- Hosted Voice
- Microsoft Teams Phone
- SIP Trunking
- Digital phone lines
- Full Fibre
- Business broadband
- Leased lines
- Mobile data
- Specialist gateways
- Replacement alarm communicators
- Digital fax
- Service retirement
We explain the benefits, limitations and costs.
6
Supplier coordination
We coordinate with relevant:
- Telecoms providers
- Internet providers
- Alarm maintainers
- Lift companies
- Door-entry suppliers
- Payment providers
- Facilities contractors
- Internal departments
Specialist equipment must be approved by its appropriate maintainer.
7
Migration and number porting
The plan covers:
- New service orders
- Installation dates
- Number porting
- Hardware
- Network changes
- User communication
- Temporary routing
- Contingency arrangements
- Contract timing
8
Testing
Testing may include:
- Incoming calls
- Outgoing calls
- Direct-dial numbers
- Call routing
- Alarm signalling
- Lift emergency calls
- Door entry
- Payment terminals
- Broadband
- Monitoring systems
- Power-loss behaviour
- Internet failover
9
Controlled cancellation
A legacy service is cancelled only when:
- The replacement is operating
- Testing is complete
- Number migration is confirmed
- Dependencies have been checked
- The service owner has approved it
- The relevant specialist has signed it off
- Evidence has been recorded
10
Ongoing support
Stratiis can continue to support:
- Hosted Voice
- Microsoft Teams Phone
- SIP Trunks
- Business connectivity
- Internet failover
- Number management
- Call routing
- Network equipment
- Future site changes
Frequently asked questions
What does PSTN stand for?
PSTN stands for Public Switched Telephone Network.
It is the traditional telephone network used to deliver analogue landline and related services.
When is the PSTN being switched off?
BT Group plans to retire the PSTN by 31 January 2027. Other providers are following broadly similar migration programmes, although their individual dates may differ.
Was the switch-off deadline delayed?
The programme previously worked towards an earlier deadline, but the current retirement date is 31 January 2027. Businesses should use the current date for planning while also checking their own provider's timetable.
Will our landline numbers disappear?
Not necessarily.
Existing business numbers can often be transferred to a new digital telephone service through number porting.
Can we keep our existing phone system?
Possibly.
A supported phone system may be connected using SIP Trunks.
An assessment should confirm compatibility, security and long-term value.
What will replace ISDN?
Possible replacements include:
- SIP Trunking
- Hosted Voice
- Microsoft Teams Phone
- Another IP-based telephone platform
The correct option depends on your existing system and future strategy.
Will alarms be affected?
Alarms using analogue telephone lines may need replacement communication equipment.
Speak to the alarm maintenance provider and test the complete service.
Will lift emergency phones be affected?
Lift phones using legacy lines may require a mobile or IP-based replacement.
The lift maintenance provider should approve and test the solution.
Will fax machines still work?
Traditional fax can be unreliable over some digital services.
A digital fax or secure document alternative may be more appropriate.
Is broadband affected?
Some copper-based broadband products are affected by the wider withdrawal of legacy infrastructure. Your provider should confirm the suitable replacement.
What happens during a power cut?
Digital services may stop when routers, switches and phone equipment lose power.
Battery backup, generators, mobile services or alternative routing may be required.
Do we need backup internet?
It should be considered where telephone calls or important equipment depend on the internet connection.
Can we use an analogue telephone adapter?
Some devices may work with a supported adapter.
Compatibility must be confirmed and tested, particularly for safety-critical equipment.
Should we wait for our provider to contact us?
No.
Your provider may not know what equipment is connected to each line.
Begin your own audit and contact all relevant equipment maintainers.
Should we cancel lines that appear unused?
No.
Trace and test each line first.
An apparently unused line may support broadband, alarms, lifts or monitoring equipment.
How long does a PSTN migration take?
A straightforward phone migration may be completed relatively quickly.
A multi-site project involving connectivity, porting, alarms, lifts and several contractors may take months.
Can Stratiis migrate our telephone numbers?
Stratiis can help audit the numbers, plan the porting process and coordinate migration to an appropriate voice service.
Can Stratiis replace our business phone system?
Yes.
Stratiis can help with Hosted Voice, Microsoft Teams Phone, SIP Trunking and Unified Communications.
Can Stratiis replace our internet connection?
Yes.
Stratiis can help with business broadband, Full Fibre, leased lines, managed routers and backup connectivity.
Can Stratiis replace lift or alarm equipment?
Stratiis can help identify connectivity requirements and coordinate the wider migration.
Specialist lift, alarm and safety equipment should be supplied, approved and tested by the appropriate qualified maintainer.
Do not let an unidentified phone line become a business emergency
The PSTN switch-off is not only about replacing office telephones.
It is about finding every system that still depends on traditional communications infrastructure.
The greatest risk may be hidden in a lift room, plant cupboard, remote office or old supplier account.
Stratiis can help you build a complete picture of your existing services and create a controlled route to digital communications.
We can review your phone systems, numbers, broadband and connected services, then coordinate migration, testing and support.
Start with an audit. Find every affected service. Complete your migration before 31 January 2027.
Call: 0141 348 7960
Email: sales@stratiis.com
