PSTN switch-off support
Find every legacy line before it becomes a problem
BT Group plans to retire its traditional PSTN network by 31 January 2027. Affected business phone, ISDN and related legacy services need a planned move to digital alternatives. The obvious office number is only part of the picture: an old line may also connect a lift, alarm, door-entry system or broadband service. Stratiis helps Scottish businesses identify dependencies, choose replacements and test each change.
What is the PSTN switch-off?
The Public Switched Telephone Network (PSTN) is the traditional network used for analogue landline calls. BT Group's retirement of that network means services dependent on its legacy PSTN, ISDN and related products must move to suitable digital services. Your telephone number may be portable, but the equipment and connection behind it need checking. The deadline applies to BT's network; other network operators can have different timetables.
The deadline
When is the UK PSTN switch-off?
BT Business and Openreach state 31 January 2027 for retirement of BT's traditional network. Their guidance is to move affected services before that date. Your provider may give you an earlier migration window, and complex services need time for supplier work, number porting and tests. The final date is the end of the transition, not a sensible date to start it.
Check the notice from each provider and what service you actually have. The wider move away from copper access networks is a separate programme: the 2027 PSTN date does not mean every FTTC or other copper-based broadband circuit stops that day. A broadband product tied to a legacy analogue line may still need migration. BT Business explains the affected legacy products; Ofcom explains the digital landline change.
The hidden risk
Which business services could be affected?
Trace every legacy line to its real use. A bill may identify a number or circuit but say little about the equipment connected to it. Infrequently used safety equipment can be especially easy to overlook.
Office calling
Analogue handsets, ISDN connected phone systems, reception lines and direct dial ranges need a calling and number plan.
Alarms and lifts
Security and fire alarms, lift emergency phones and refuge telephones may use a line to reach a monitoring or response service. Prioritise specialist review.
Access and monitoring
Door entry, intercoms, CCTV, plant room alerts and remote monitoring may be owned by facilities teams or contractors rather than IT.
Transactions and fax
Older payment terminals or fax machines may use analogue signalling. Their suppliers should confirm a supported replacement and test it.
Broadband dependencies
Some older data services are linked to a legacy telephone line. Confirm the exact product before changing or cancelling the voice service.
Remote sites
A small branch, temporary location or outbuilding may have a line billed under an old account and no obvious internal owner.
Safety first
How should alarms, lift phones and other critical devices move?
Identify the device, line, maintainer and response destination. Ask its specialist supplier whether it supports IP or mobile connectivity, whether hardware or certification changes are required, and how power and network failures will be handled. Test the complete journey with the monitoring centre or emergency response process before the old line is removed.
Do not assume an analogue telephone adapter makes every alarm, fax or lift communicator compatible. The equipment supplier must confirm the proposed service and sign off the result. Where vulnerable people or emergency communications depend on a line, make that dependency visible and prioritise a controlled migration. Ofcom's digital landline guidance also explains why power backup matters.
Physical audit
Inspect the lift room, alarm panel, reception, plant room, communications cabinet and remote buildings. Match each connection to bills and maintenance records.
Acceptance test
Prove the device reaches its intended destination, works under the agreed failure scenarios and has an owner who approves the change.
Inventory
What should a PSTN switch-off audit include?
A useful audit combines provider invoices, number lists, contracts and site checks. For each service, record its number or circuit reference, site and exact location, connected device, supplier, internal owner, business importance and proposed replacement. Add the migration date, test evidence and approval to cancel the legacy service.
Billing alone is incomplete because the provider may know the line but not the third-party equipment attached to it. The aim is a working register that can be handed between IT, facilities, property, finance and specialist maintainers.
| Service | What to record | Who confirms the replacement? |
|---|---|---|
| Business numbers | Provider, account, number ranges, call flows and any linked broadband. | Telecoms owner and receiving provider after porting tests. |
| Lift or alarm line | Device location, maintainer, monitoring destination and power needs. | Lift or alarm specialist and the internal safety owner. |
| Data or broadband | Product type, line dependencies, router and site importance. | Connectivity provider and site owner after service tests. |
| Payment or monitoring | Device model, connection type, vendor and continuity needs. | Equipment supplier and the operational owner. |
Replacement choices
What can replace an analogue or ISDN business phone system?
The answer depends on the condition of your existing system, the way employees work and how complex incoming calls are. Keeping a supported system may be practical; replacing an ageing one may be better value. Separately, each non-voice device needs a supported connection approved by its maintainer.
| Option | Where it fits | What to check |
|---|---|---|
| Hosted voice | A cloud phone system for business numbers, routing and calling across devices and sites. | Call flows, connectivity, licences and compatible devices. Explore Hosted Voice. |
| Microsoft Teams Phone | External calling through Teams for organisations already working in Microsoft 365. | Calling connection, licensing and frontline needs. Explore Microsoft Teams Phone. |
| SIP Trunking | A compatible, supported on-site phone system can connect to an IP voice service without immediate replacement. | Manufacturer support, SIP compatibility, network quality, resilience and the remaining life of the system. |
| Digital or mobile service | A simpler phone line or specialist IP/mobile communicator may fit a low-volume or equipment-specific use. | Device compatibility, coverage, power and supplier approval. |
Explore the SIP Trunking option in this comparison, or ask Stratiis to assess whether retaining your current phone system is practical.
Numbers and broadband
Can you keep your existing telephone numbers?
Often, yes. Established business numbers can commonly be ported to a suitable new provider. Check the account name, service address, complete number range, direct dials and services linked to the current line before arranging the move. The old service should remain active until the port and essential calls have been confirmed.
Broadband needs its own check. Some ADSL and other products run over legacy line arrangements, while an FTTC connection may continue using a different digital broadband product such as SoGEA. Full Fibre may be available at some sites, but it is not the only possible route. Choose the replacement based on the actual circuit and what the provider can supply at that address.
Continuity
What happens during a power cut or internet outage?
Traditional analogue phones could often draw power from the telephone network. Digital calling generally depends on powered local equipment such as a router, network switch or IP phone. A cloud platform may remain online when your office loses power or connectivity, but local devices may not. A critical alarm or emergency phone needs a specialist continuity plan.
Match the backup to the consequence of failure: power protection, a second fixed connection, mobile failover, alternate routing or another location may be appropriate. Test the specific calls and connected devices, including what happens when one path fails. Explore internet failover.
Different premises
Who needs to be involved in a multi-site migration?
IT rarely owns every affected line. Housing associations may need property, repairs, telecare, lift and door-entry suppliers across many developments. Professional services firms may need to protect direct dial ranges and reception. Charities in shared premises should confirm which lines and devices belong to the landlord. Multi-site organisations need one register and consistent sign-off at every location.
Assign an internal owner to each service and ask the equipment specialist to approve safety-critical replacements. A site is complete only when its new service has passed the agreed test and the old service can be cancelled safely.
Find hidden lines
Investigate unfamiliar charges and inspect locations where equipment rarely receives attention.
Keep the number plan
Check every direct dial, main number and linked service before a port.
Prove the replacement
Record tests for calls, alarms, lifts, data connections and failure scenarios.
Control cancellation
Cease a legacy line only after the owner and relevant supplier approve it.
Avoid disruption
What mistakes create the greatest switch-off risk?
Waiting until a migration notice arrives, reviewing only the office handsets, assuming a bill shows what is connected and cancelling a line that appears unused all leave gaps. An adapter that makes a dial tone is not proof that an alarm, fax or payment terminal will work reliably. A replacement is complete only after its actual function and failure behaviour are tested.
Acting early leaves time to resolve rejected number ports, order connectivity and coordinate third-party maintainers. It also gives you a chance to remove genuinely unused services after their dependencies are ruled out.
Our process
How Stratiis plans a PSTN migration
We start with a service register and work towards a controlled change for each affected line.
Discover
Collect numbers, bills, contracts, sites and known equipment.
Trace
Inspect connections and identify the owner and maintainer for each service.
Prioritise
Assess safety, operational impact, power and network dependencies.
Design
Select supported digital replacements and agree supplier responsibilities.
Migrate
Plan number ports, installations, contingency routes and testing.
Sign off
Prove the new service before approved cancellation of the old line.
Frequently asked questions
PSTN switch-off questions, answered
Direct answers to the issues that matter most when planning a business migration.
What does PSTN stand for?
Public Switched Telephone Network. It is the traditional network used to carry analogue landline calls and support some connected services.
When is BT's PSTN switch-off?
BT Group plans to retire its traditional PSTN by 31 January 2027. Providers can schedule customer migrations earlier, and other networks may have different dates.
Was the deadline delayed?
Yes. The earlier target was the end of 2025. BT Group's current published deadline is 31 January 2027. Plan to finish before your provider's cutover, rather than relying on the last day.
Will our landline number disappear?
Not necessarily. Many business numbers can be ported to a digital voice provider. Eligibility and account details should be confirmed before cancelling the existing service.
Can we keep our current phone system?
Possibly, if it is supported and compatible with a digital calling connection such as SIP Trunking. Compare the replacement options and assess its remaining useful life.
What replaces ISDN?
Depending on the system, a business might use SIP Trunking, Hosted Voice, Microsoft Teams Phone or another suitable digital service. Number migration and call routing need planning.
Will security alarms be affected?
An alarm using an analogue line may be affected. Ask its maintainer to identify the connection, approve an IP or mobile replacement where suitable and test communication with the monitoring centre.
Will lift emergency phones be affected?
Some lift phones rely on legacy lines. The lift maintainer should confirm the replacement, power and signal resilience, emergency call destination and sign-off tests.
Will fax machines still work?
Not every fax machine works reliably over a digital voice adapter. Consider a supported digital fax or different secure workflow, and test any fax service that must remain.
Is all copper broadband switching off in January 2027?
No. PSTN retirement and full copper retirement are different programmes. Broadband tied to a legacy line may need migration, while some FTTC services can continue via a digital broadband product. Check the exact service with its provider.
What happens during a power cut?
Digital phones and routers typically need local power. Plan suitable battery or other backup, and test critical communications under the expected failure conditions.
Do we need backup internet?
It depends on the impact of losing calls or connected services. A second link, mobile failover or alternative routing may reduce risk, but each needs testing.
Can we use an analogue telephone adapter?
Sometimes, but an adapter is not proof that specialist equipment will work correctly. The device supplier must confirm compatibility and the end-to-end test.
Should we wait for our provider to contact us?
No. Ask the provider about your services, but also inspect your own sites and speak to alarm, lift, payment and property suppliers. A provider may not know what is attached to each line.
Should we cancel lines that appear unused?
Only after tracing them, testing any suspected device and getting the service owner's approval. An emergency device may rarely place a call.
How long does migration take?
It varies with the number of sites, equipment suppliers, replacement connections and number ports. Start the inventory now and set a schedule for each service.
Can Stratiis migrate our phone numbers?
We can assess the numbers, coordinate an appropriate porting plan and test calls after the move, subject to provider and number eligibility.
Can Stratiis replace the business phone system?
We can assess Hosted Voice, Microsoft Teams Phone or a suitable retained-system option.
Can Stratiis replace our internet connection?
We can review connectivity and propose an appropriate replacement or resilience option alongside the voice migration.
Can Stratiis replace lift or alarm equipment?
Specialist lift and alarm maintainers should select, install and approve their equipment. Stratiis can help identify dependencies and coordinate the communications side with them.
Start with an audit
Do not let an unidentified line become an emergency
We can review your telephone services, numbers, broadband and connected equipment, then build a migration register with owners, tests and sign-off. Find the affected lines and plan their move before the 31 January 2027 deadline.
Book a PSTN Switch-Off AuditCall 0141 348 7960
Or email sales@stratiis.com.
