PSTN Switch-Off UK: Business VoIP Migration Guide

UK businesses must move PSTN and ISDN services to digital alternatives before the 31 January 2027 deadline. Start by auditing phone lines, numbers, alarms, lifts, fax, card machines and door entry systems, then plan number porting, VoIP migration, resilience, emergency calling and supplier testing before cancelling legacy services after go-live.

Last updated: June 2026
Reviewed by: CompareServices Editorial Team
Reading time: 18–20 minutes

Quick Verdict

The PSTN switch-off is a business continuity project, not just a telephone upgrade. The safest approach is to audit every phone line, number and connected device before choosing a digital voice route. For most UK SMEs, the replacement will be a cloud VoIP or hosted PBX system. Businesses with existing PBX investment may use SIP trunking, while Microsoft 365-led teams may choose Teams Phone through Operator Connect or Direct Routing.

Openreach says the existing analogue network is being retired by 31 January 2027, and GOV.UK’s connectivity timeline says users of the Openreach PSTN need to move to new services by that date. Businesses should still check supplier-specific migration dates because some providers may move customers earlier.

Business situation	Best action	Why it matters	Check before cancelling old lines
Using PSTN or ISDN for calls	Move to cloud VoIP, hosted PBX, Teams Phone, SIP or hybrid	Legacy voice services are being retired	Number porting, call routing, go-live testing
Existing PBX still in use	Assess SIP trunking, hosted PBX or staged replacement	The PBX may depend on ISDN or analogue services	PBX compatibility, support contract, security updates
Alarms, lifts, fax or payment terminals connected	Speak to the device supplier before migration	These may fail if the old line is removed without replacement	Digital alternative, GSM/IP route, test certificate
Multiple sites or old number ranges	Create a site-by-site migration plan	Unmapped numbers can delay porting or break call flows	Supplier records, ownership, active services
Phones must work during outages	Plan power backup and failover routing	Digital voice relies on powered equipment and connectivity	UPS, mobile fallback, backup broadband, emergency address data

Important: do not cancel existing phone services until your new system is live, key numbers are ported, legacy devices are tested and emergency-calling behaviour is understood.

Why Trust CompareServices?

CompareServices is an independent UK business services comparison platform. This guide is designed for business owners, operations managers, IT teams and procurement leads who need to prepare for the PSTN switch-off without confusing provider sales messaging with a migration plan.

Our approach is to separate the migration decision into practical checks: what you currently use, what must be replaced, which digital route fits your business, which devices need specialist handling, and which risks must be tested before legacy services are removed.

UK business-focused guidance rather than consumer landline advice
Clear separation between phone systems, broadband, SIP, Teams Phone and legacy devices
Practical audit and checklist format for migration planning
Related guides limited to live CompareServices pages only

What Is The PSTN Switch-Off?

The PSTN switch-off is the retirement of the UK’s older analogue Public Switched Telephone Network and related legacy services such as ISDN. Instead of calls being carried over traditional copper voice lines, businesses will use digital services delivered over internet protocol, fibre-based networks, SIP trunks or hosted platforms.

UK PSTN switch-off migration checklist for business phone systems, alarms, lifts, fax and VoIP — **PSTN switch-off planning:** businesses should audit phone numbers, connected devices, emergency calling, failover and supplier responsibilities before moving to digital voice.

For many businesses, the change will be straightforward: move from a traditional phone line to a cloud phone system or hosted VoIP service. For others, the project is more complex because old lines may be connected to alarms, lifts, payment terminals, fax machines, door-entry systems, monitoring equipment or legacy PBX hardware.

The key mistake is assuming the office handset system is the only thing affected. A business may have one visible phone system but several hidden PSTN-dependent services across sites, outbuildings, tills, reception areas, lifts or alarm panels.

What is being retired?

Traditional analogue PSTN lines
ISDN2 and ISDN30 services
WLR-linked traditional voice services
Some older broadband/voice bundles that depend on legacy line rental
Legacy PBX connectivity that depends on ISDN or analogue lines

What replaces it?

Cloud VoIP or hosted phone systems
Hosted PBX platforms
Microsoft Teams Phone with a suitable calling route
SIP trunking for compatible PBX systems
IP, fibre, GSM or specialist replacements for non-voice devices
Data-only broadband such as FTTP, SOGEA or leased-line connectivity where suitable

Who Is Affected?

Any UK business still using traditional landlines, ISDN, WLR-linked services or PSTN-connected equipment should review its setup. The risk is higher when phone services have been in place for many years, supplier records are incomplete, or different sites have different contracts.

Affected area	Examples	Risk if ignored	Owner to involve
Business voice calling	Main numbers, DDIs, reception lines, branch numbers	Lost calls, failed porting, customer disruption	Telecoms provider, IT, operations
PBX and extensions	ISDN-connected PBX, old handsets, hunt groups	Internal calling and routing may fail	Telephony maintainer, IT partner
Safety systems	Lift emergency phones, fire panels, alarm diallers	Safety or compliance failure	Lift, alarm, fire or facilities supplier
Payment and retail devices	PDQ terminals, tills, franking machines	Payment interruption or transaction failure	Payment provider, finance, retail ops
Legacy communications	Fax, modems, remote monitoring	Lost documents, failed alerts or monitoring gaps	Device vendor, IT, compliance lead
Emergency calling	999/112 address data, power resilience	Incorrect location or unavailable calling during outage	Telecoms provider, health and safety lead

Practical rule: if a device dials a number, receives a call, sends an alert or relies on a phone line, treat it as part of the PSTN migration audit until confirmed otherwise.

Digital Migration Routes Compared

There is no single replacement that fits every business. The right digital route depends on whether you want a fully managed cloud system, need Microsoft Teams integration, want to keep existing PBX hardware, or must migrate in phases.

Migration route	Best for	Main benefit	Main watch-out
Cloud VoIP	Most SMEs replacing landlines	Fast setup, app-based calling, simple user management	Requires suitable broadband and device testing
Hosted PBX	Office teams needing extensions and routing	Familiar PBX-style features without on-site hardware	Check call-flow limits and support model
Microsoft Teams Phone	Microsoft 365-first businesses	Calling inside Teams with Operator Connect or Direct Routing	Licensing and implementation route need careful planning
SIP trunking	Businesses keeping compatible PBX hardware	Replaces ISDN while retaining existing PBX investment	Needs technical ownership, PBX compatibility and resilience design
Hybrid migration	Multi-site or phased estates	Allows staged migration across sites and systems	Can create complexity unless the final end-state is defined
Specialist device replacement	Alarms, lifts, fax, PDQ and monitoring	Moves non-voice devices away from analogue dependency	Must be validated by the device supplier, not only the phone provider

When cloud VoIP is usually enough

Cloud VoIP is usually enough when the business has simple office calling, mobile staff, a small number of locations, and no complex PBX dependency. It is often the most practical route for SMEs that want to replace traditional lines quickly and manage users through an online portal.

When SIP trunking may be better

SIP trunking may be better when a business has already invested in a compatible PBX, has an IT team or telecoms partner to manage it, or needs a phased migration away from ISDN. SIP is not the simplest route for non-technical buyers, but it can be a strong fit for existing infrastructure.

When Teams Phone makes sense

Teams Phone makes sense when Microsoft Teams is already the business’s daily communications hub. The decision is less about replacing a handset and more about choosing the correct calling route: Microsoft Calling Plans, Operator Connect or Direct Routing.

Line And Device Audit: What To Check First

The audit is the most important part of the project. It reduces the risk of missed services, failed number ports and unexpected outages.

Phone numbers and contracts

Main published business numbers
Direct dial numbers and number ranges
Non-geographic numbers such as 03 or 08 numbers
Fax numbers and historical numbers still receiving calls
Numbers assigned to branches, departments or remote sites
Current supplier, account number and contract end date
Any number used in adverts, websites, signage or printed material

Existing phone system

PBX make, model and support status
ISDN channels or analogue lines feeding the system
Desk phones and conference phones
Reception, hunt groups, call queues and voicemail routing
Call recording, reporting or CRM integration
Out-of-hours routing and emergency contact flows

Hidden or non-obvious services

Alarms, monitoring and remote alerts
Lift emergency telephones
Fire panels and safety systems
Door entry and gate systems
Fax machines and analogue modems
PDQ/card machines and tills
Franking machines and older office equipment
Backup lines that are billed but rarely used

Best practice: build a simple spreadsheet with line number, service type, site, supplier, monthly cost, contract date, owner, migration action and test result.

How Number Porting Fits Into PSTN Migration

Number porting is the process of moving existing business numbers from one provider to another. It is often straightforward, but it can become difficult if records are wrong, numbers have been cancelled, services are bundled, or the current supplier details do not match the porting request.

Before requesting a port

Confirm every number that needs to move
Check whether the number is active and who currently bills it
Match the business name and address to supplier records
Identify whether numbers are single lines or part of a range
Check whether broadband, alarms or other services depend on the same line
Ask the new provider how calls will route during and after porting

During porting

Keep old services active until the port is complete
Agree the port date and test window
Prepare temporary forwarding if needed
Test inbound calls from mobile and landline networks
Test outbound caller ID after the number moves
Document any numbers that fail or need resubmission

After porting

Check every main number and direct dial number
Confirm department routing, voicemail and out-of-hours rules
Check emergency address records where applicable
Confirm old lines can be ceased only after device testing
Update supplier records and internal documentation

Avoid this mistake: never cancel a line because you assume the number has moved. Confirm port completion, call routing and any dependent devices first.

Beyond Voice: Alarms, Lifts, Fax, PDQ And Door Entry

Many PSTN switch-off risks come from devices that are not usually managed by the phone-system provider. These devices may have been installed by facilities, security, payment, property or safety suppliers years before the VoIP migration project begins.

Device or service	Typical issue	Possible replacement route	Who should confirm?
Lift emergency phone	May dial out over an analogue line	GSM, IP or specialist lift-line replacement	Lift maintenance supplier
Alarm dialler	May send alerts over PSTN	IP or mobile communicator	Alarm/security company
Fire panel	May report events over old line	Approved digital or mobile monitoring route	Fire safety supplier
Fax machine	Analogue fax may be unreliable over VoIP	Cloud fax, secure email or process replacement	IT/compliance owner
PDQ/card terminal	Older terminals may rely on dial-up	IP, Wi-Fi or mobile payment terminal	Payment provider
Door entry or gate	May call a handset or mobile via line	IP or mobile-enabled access system	Access-control supplier
Remote monitoring	Alerts may fail if line is removed	IP monitoring, SIM route or vendor replacement	Equipment vendor

For critical devices, do not rely on a general phone-system quote. Ask the device supplier to confirm the correct migration method, installation requirements, testing process and any compliance certificate or service record needed after the change.

Step-By-Step Business VoIP Migration Plan

A practical migration plan should move from discovery to testing. The timeline below is a safe planning model; simple businesses may move faster, while multi-site or safety-critical estates need more time.

Stage	Main actions	Output
1. Discovery	List numbers, lines, sites, devices, suppliers, contracts and call flows	Line and device audit
2. Requirement design	Define users, departments, routing, voicemail, recording, apps and handsets	Target phone-system design
3. Supplier selection	Compare cloud VoIP, hosted PBX, Teams Phone, SIP or hybrid routes	Preferred migration route and quote
4. Connectivity check	Assess broadband, router, Wi-Fi, QoS, backup and power resilience	Call-quality readiness plan
5. Configuration	Create users, call flows, greetings, business hours, voicemail and caller ID	Configured test environment
6. Number porting	Submit port request, agree date, keep legacy lines active	Numbers moved to new provider
7. Device migration	Replace or reroute alarms, lifts, fax, PDQ, door entry and monitoring	Supplier-tested device replacements
8. Go-live testing	Test inbound/outbound calls, emergency info, failover and user workflows	Signed-off migration
9. Legacy cancellation	Cancel old services only after testing and documentation	Reduced risk and cleaner billing

Training users before go-live

Staff should understand how to answer calls, transfer calls, use voicemail, change status, use mobile apps, access recordings and report call-quality issues. Even a good phone system can fail operationally if users are not trained before the switch.

Testing call flows

Test the real customer journey, not only whether one handset rings. Call main numbers, department options, direct dials, out-of-hours routes and overflow rules from different networks. Test mobile users and remote staff separately.

999, Emergency Calling And Power Cuts

Digital voice services can support emergency calling, but businesses must understand what happens if broadband or power fails. Traditional analogue phones could sometimes continue to work during a local power cut because power came from the exchange. Digital voice depends on powered equipment such as routers, switches, phones, ONTs and Wi-Fi access points.

Ofcom has published guidance around protecting access to emergency services during power cuts. For businesses, the practical point is clear: ask the provider how emergency calls work, how location/address data is maintained, and what resilience options are available for sites where phone access is critical.

Emergency-calling checks

Confirm 999/112 support with the chosen provider
Check address data for each site or remote user group
Understand whether remote workers present the office location or another address
Document what happens if broadband is down
Document what happens if power is down
Plan battery backup or alternative routes for critical sites

Power and failover options

UPS battery backup for router, firewall, switches and ONT
Mobile failover for inbound calls
Backup broadband or leased-line resilience
Call forwarding to mobiles during site outages
Secondary site routing for multi-location businesses
Documented escalation route for service failures

Compliance note: this page provides buyer guidance, not legal advice. Businesses with safety-critical systems, regulated operations or vulnerable users should confirm obligations with qualified advisers and the relevant device/provider specialists.

Costs, Contracts And Quote Checks

A PSTN migration quote should show more than a monthly user licence. The full project may include number porting, handsets, headsets, setup, training, call recording, storage, broadband upgrades, router changes, device replacements and support.

Cost area	Questions to ask	Risk if missed
User licences	What features are included per user and what costs extra?	Low headline price becomes expensive after add-ons
Numbers and porting	Are number rental, porting and port-away charges listed?	Unexpected charges or delays during migration
Hardware	Are desk phones, headsets, conference devices or adapters included?	Users cannot work effectively at go-live
Connectivity	Does the current broadband support the expected call volume?	Call-quality issues and dropped calls
Legacy devices	Who pays for alarm, lift, fax, door entry or payment terminal migration?	Operational or safety-critical services fail
Support and training	Is migration support, user training and admin handover included?	System works technically but staff cannot use it properly
Contract terms	What is the minimum term, renewal process and price-change clause?	Long-term cost or exit risk

Quote comparison guardrails

Compare total first-year cost, not only per-user monthly cost
Ask whether VAT is included or excluded
Ask whether call recording, call queues and analytics are included
Ask whether onboarding and porting support are included
Ask whether hardware is rented, financed or purchased
Ask whether you can reduce users during the contract
Ask what happens if migration is delayed by number porting or third-party devices

Common PSTN Migration Mistakes To Avoid

Only auditing desk phones: many risks sit in alarms, lifts, fax, PDQ, door entry and monitoring devices.
Cancelling lines too early: this can risk losing numbers or breaking dependent services.
Ignoring broadband readiness: cloud calling needs stable upload, low latency, low jitter and reliable local networking.
Choosing the cheapest user licence: key features such as recording, queues, failover or admin controls may cost extra.
Not testing out-of-hours calls: customers often discover routing issues only after the first evening or weekend.
Leaving emergency calling unclear: address data, remote workers and power-cut behaviour must be understood.
Assuming every device can use VoIP directly: some analogue devices need replacement rather than simple conversion.
Not documenting the final setup: future support becomes harder if no one knows which numbers, users and devices moved.

PSTN Migration Checklist For UK Businesses

Use this checklist before approving a provider quote or setting a port date.

Audit checklist

All active phone numbers listed
All direct dial numbers and number ranges listed
All suppliers and account numbers recorded
Contract dates and cancellation terms checked
PBX make, model and support status confirmed
Alarms, lifts, fax, PDQ, door entry and monitoring devices checked
Current monthly costs recorded
Broadband and router readiness checked

Migration checklist

Digital route selected: cloud VoIP, hosted PBX, Teams Phone, SIP or hybrid
Call flows documented for main hours and out-of-hours
User list, extensions and permissions agreed
Number porting documentation prepared
Temporary routing or forwarding agreed where needed
Legacy-device suppliers contacted
Emergency-calling and address data reviewed
Power and broadband failover options agreed

Go-live checklist

Inbound calls tested to every main number
Outbound caller ID tested
Direct dial numbers tested
Auto-attendant and routing tested
Voicemail and missed-call alerts tested
Mobile apps and remote users tested
Alarms, lifts, fax, payment terminals and door entry tested separately
Old services cancelled only after sign-off

Official References Checked

This guide has been prepared using current UK public guidance from official and primary sources. Businesses should still confirm their own supplier timetable and contractual position before making changes.

Frequently Asked Questions

What is the PSTN switch-off in the UK?

The PSTN switch-off is the retirement of the UK’s older analogue phone network and related ISDN services. Businesses still using traditional phone lines need to move voice calling and connected devices to suitable digital alternatives before the January 2027 deadline.

When is the PSTN switch-off deadline?

The key UK deadline is 31 January 2027 for users of the Openreach PSTN. Some providers may move customers earlier, so businesses should check their own supplier dates and avoid waiting until the final months.

Does the PSTN switch-off affect business broadband?

It can. Older broadband products tied to traditional phone lines may need replacing with data-only or fibre-based services. Businesses should check whether their broadband, phone numbers, alarms, payment terminals or other devices still depend on an analogue line.

Do I need to move to VoIP before the PSTN switch-off?

Most businesses replacing traditional landlines or ISDN will move to a digital voice service such as cloud VoIP, hosted PBX, Microsoft Teams Phone, SIP trunking or another IP-based route. The right option depends on your current setup and call requirements.

Can I keep my existing business phone numbers?

In many cases, yes. Existing business numbers can usually be ported to a new provider, but you should confirm ownership, active services, required documentation, expected timing and whether any temporary routing is needed during migration.

What business devices may be affected by the PSTN switch-off?

Affected devices may include fax machines, alarm diallers, lift emergency phones, door entry systems, fire panels, payment terminals, franking machines, telecare devices and remote monitoring equipment. Each should be checked with the relevant supplier before migration.

What happens to 999 calls after moving to VoIP?

VoIP services can support emergency calling, but businesses must ensure correct address information, power resilience and failover plans are in place. Emergency-calling obligations and outage behaviour should be confirmed with the chosen provider before go-live.

Will a cloud phone system work during a power cut?

A cloud phone system depends on powered equipment such as routers, switches, handsets and internet access. Businesses that rely on phone service during outages should plan battery backup, mobile failover, alternative routing or a secondary connection.

How long does business VoIP migration take?

A simple small-business migration may be completed quickly once requirements are known, but number porting, device checks, call-flow design, training and testing can extend the project. Multi-site or device-heavy estates should plan several weeks or more.

Should I cancel my existing phone lines before porting numbers?

No. Do not cancel old lines before confirming number porting and go-live. Cancelling too early can risk losing numbers or interrupting connected services. Keep legacy services active until the migration is tested and signed off.

Is SIP trunking still relevant after the PSTN switch-off?

Yes. SIP trunking can be a suitable digital route for businesses keeping compatible PBX infrastructure. It is different from a fully hosted cloud phone system and is better suited to IT-managed or existing PBX environments.

What is the safest first step for a business?

Start with a line and device audit. List every phone number, supplier, contract, device and location that may use PSTN or ISDN. This reduces migration risk and helps providers quote accurately.

Only live and relevant related guides are listed here. More telecoms guides can be added after they are published and indexable.

Guide	Why read it next?
Business Phone Systems UK — Complete Comparison Guide	Compare cloud VoIP, hosted PBX, UCaaS, Teams Phone, SIP and hybrid business phone-system routes.
Cloud Phone System UK — Complete Comparison Guide	Review cloud-hosted phone-system options, providers, features, setup checks and pricing factors.

Get Help Comparing PSTN Replacement Options

CompareServices helps UK businesses compare phone-system and digital voice options without relying on a single supplier recommendation. If you are unsure whether to choose cloud VoIP, hosted PBX, Teams Phone, SIP trunking or a phased hybrid migration, start with your line and device audit.

What you can compare:

PSTN and ISDN replacement routes
Cloud VoIP and hosted PBX options
Teams Phone, SIP and hybrid suitability
Number porting and migration support
Legacy-device risk and supplier responsibilities
First-year costs, contract terms and support levels

Start comparing business phone system options now.

Four Workstreams Every Business Should Check

Line & Number Audit

VoIP Migration Route

Legacy Device Plan

Resilience & Testing