PSTN Switch-Off UK: Business Migration Guide for 2027
Prepare your business phone lines, ISDN services, fax machines, alarms, lift lines, PDQ terminals and digital voice migration before the UK analogue network is retired.
The UK PSTN switch-off means analogue and ISDN services are being replaced by digital voice and IP-based connectivity by 31 January 2027. Businesses should audit every phone line, number, alarm, lift, fax, payment terminal and broadband dependency before migration to avoid service disruption, number loss and emergency-calling gaps.
Identify all PSTN-dependent services before any line cancellation, number port or digital voice cutover.
The Analogue Phone Network Is Being Replaced by Digital Voice
Legacy copper voice services and ISDN lines were designed for older telephone systems. Business communications now need digital voice, cloud calling, SIP, mobile continuity, broadband resilience and verified emergency-calling details.
The analogue network retirement creates a fixed planning window for business migration.
Voice moves to broadband-style IP connectivity, VoIP, SIP or digital landline services.
Emergency calling needs address accuracy, local power, broadband and failover consideration.
What Could Break When Legacy Lines Are Removed?
The safest migration starts by mapping every line, number, device and supplier contract. Do not assume that a device works over VoIP until the manufacturer or maintainer has confirmed the replacement route.
| Legacy Service or Device | Why It Matters | Migration Route | Risk Control |
|---|---|---|---|
| Analogue business line | Traditional voice service will not continue in the same form. | Digital landline, cloud VoIP or hosted phone system. | Keep service active until number porting and test calls complete. |
| ISDN2 / ISDN30 PBX | Legacy PBX trunks need replacing before withdrawal. | SIP trunks, hosted PBX, 3CX, Teams Phone or hybrid migration. | Audit channels, DDI ranges, hunt groups and call routing. |
| Fax machine | Fax can be unreliable over ordinary VoIP paths. | Digital fax workflow, secure document process or tested ATA route. | Replace fax dependency where practical; test any adapter route. |
| Lift emergency phone | Safety-critical service may depend on line power and monitoring. | Specialist lift provider upgrade, cellular unit or tested IP route. | Coordinate with lift maintainer before telecom changes. |
| Fire / intruder alarm panel | Alarm signalling may fail if moved without vendor testing. | Alarm provider upgrade, IP signalling or cellular monitoring. | Request written confirmation from the alarm maintainer. |
| PDQ / payment terminal | Older payment terminals may use dial-up or analogue paths. | Ethernet, WiFi or cellular payment terminal replacement. | Confirm with payment provider before line removal. |
| Door entry / intercom | Access control may depend on a dialler or analogue port. | IP intercom, GSM/cellular module or approved adapter. | Test entry, release and emergency access workflows. |
| Monitoring diallers and out-of-hours systems | Hidden line use is often missed during office phone migrations. | IP monitoring, cellular device or software alerting. | Trace bills and line labels before cancellation. |
Choose the Right Replacement Before Porting Numbers
PSTN replacement is not one-size-fits-all. A small office may only need a digital landline or cloud VoIP route, while a multi-site estate may need SIP trunks, leased line connectivity, mobile failover and staged device replacement.
| Migration Route | Best For | Advantages | Checks Before Go-Live |
|---|---|---|---|
| Digital Landline | Small sites needing a simple line replacement. | Familiar voice experience with modern network delivery. | Router location, number retention, power backup and handset compatibility. |
| Cloud VoIP Phone System | SMEs wanting extensions, apps, queues and flexible working. | Scalable users, call routing, mobile apps, voicemail and analytics. | Broadband quality, router, QoS, porting and user training. |
| SIP Trunking | Businesses retaining a compatible PBX or 3CX system. | Keeps selected infrastructure while replacing ISDN channels. | PBX support, SIP security, firewall, DDI ranges and failover. |
| Microsoft Teams Phone Route | Microsoft 365-first organisations. | Teams as the calling interface with Calling Plans, Operator Connect or Direct Routing options. | Licences, emergency addresses, call queues, recording and network readiness. |
| Specialist Device Upgrade | Alarms, lifts, PDQ, fax, door entry and monitored systems. | Uses a vendor-approved route rather than forcing everything through VoIP. | Manufacturer approval, maintainer testing and sign-off records. |
| 4G/5G Cellular Backup | Continuity and hard-to-wire locations. | Alternative path when fixed broadband, router or line services fail. | Signal strength, router compatibility, data usage and failover testing. |
Audit the Whole Estate, Not Just the Main Phone Number
These checks help identify hidden PSTN risk before any porting order, broadband change or supplier cancellation.
Line Inventory
Match every billed line, number, DDI, fax and device connection against real usage.
PBX & ISDN Review
Check ISDN2, ISDN30, DDI ranges, hunt groups and PBX compatibility with SIP or cloud voice.
Emergency Details
Validate site addresses, critical users, emergency calling routes and outage procedures.
Power Backup
Review router, ONT, switch, handset and alarm-panel power dependencies after migration.
Adapter Caution
Use analogue adapters only where the device provider confirms they are suitable.
Cellular Continuity
Test 4G/5G failover for critical sites, temporary offices and emergency contact workflows.
Recording Governance
Check call recording, retention, PCI-safe controls and role-based access during migration.
Porting Sequence
Plan number porting after inventory, compatibility testing and customer-facing routing checks.
PSTN Switch-Off Readiness Auditor
Use this quick tool to identify whether your current setup looks suitable for a simple digital line migration, a cloud VoIP migration, SIP trunking or a deeper device dependency audit.
PSTN Risk Looks Different in Every Organisation
Different sectors use old phone lines in different ways. The migration plan should reflect safety, compliance, site resilience and customer contact risk.
Plan for 999/112, Power Cuts and Broadband Outages
Digital voice relies on local equipment such as routers, ONTs, switches and handsets. If those devices lose power or broadband fails, ordinary digital calling may stop unless backup or alternative routing is in place.
- Validate emergency service address details for each site and user type.
- Use UPS backup for router, ONT, switch and critical handsets where appropriate.
- Plan mobile rerouting, 4G/5G backup or alternative contact procedures.
- Identify users and locations with weak mobile coverage or essential landline reliance.
Keep Numbers Safe During the Move
Number migration should happen in a controlled sequence. Cancelling the old line or provider account too early can create avoidable downtime or number recovery problems.
- Match numbers against bills, line records, DDI ranges and live call flows.
- Confirm gaining and losing provider details before port submission.
- Schedule cutover windows for lower-risk business periods.
- Test inbound calls, outbound calls, caller ID, voicemail and routing immediately after migration.
Six Controlled Steps to PSTN Switch-Off Readiness
A successful migration uses discovery, testing and staged cutover rather than last-minute line cancellation.
Discover
Identify every line, number, ISDN circuit, PBX trunk, alarm and analogue device.
Classify
Group each item as voice, broadband-linked, safety-critical, payment, monitoring or unknown.
Design
Choose digital landline, cloud VoIP, SIP, Teams, cellular or specialist device replacement.
Prepare
Configure broadband, router, QoS, emergency addresses, users, routing and failover.
Port & Test
Move numbers in controlled windows and test calls, devices, alarms and continuity paths.
Retire
Cease legacy services only after confirmation, documentation and post-cutover monitoring.
Questions Before You Retire Legacy Lines?
These answers cover the 2027 switch-off, ISDN, WLR, number porting, broadband, alarms, lift phones, fax, power cuts and business migration planning.
Compare Phone System RoutesWhen is the UK PSTN switch-off?
The UK analogue phone network is scheduled to be retired by 31 January 2027. Businesses should use the remaining time to audit lines, ISDN services, numbers, broadband dependencies and any devices that still rely on old telephone connections.
Does the PSTN switch-off affect ISDN lines?
Yes. ISDN2 and ISDN30 are part of the legacy voice estate that businesses should replace with SIP trunks, cloud VoIP, Hosted PBX, Microsoft Teams Phone routing or another suitable digital voice architecture.
Can we keep our existing business numbers?
Usually, yes. Eligible UK business numbers can normally be ported to a new provider or digital phone service. Do not cancel the current line or account before the port is complete and tested.
Will fax machines, alarms or lift phones work after migration?
Not automatically. Fax, alarms, lift emergency phones, door entry systems and PDQ terminals must be checked with the device manufacturer, maintainer or payment provider before the legacy line is removed.
Will digital voice work during a power cut?
Digital voice depends on local power for routers, ONTs, switches and handsets. Critical locations should plan UPS backup, mobile failover, alternative contact routes and emergency calling procedures.
What should businesses do first?
Start with a line and device inventory. Match bills to live numbers, check ISDN/PBX dependencies, identify hidden analogue devices and confirm broadband readiness before choosing the replacement route.
Is PSTN migration the same as moving to VoIP?
VoIP is one common replacement route, but migration can also involve SIP trunks, digital landlines, Teams Phone, mobile backup, specialist alarm upgrades or hybrid solutions depending on the business estate.
Make Your Business Ready Before Legacy Lines Are Retired
Tell us about your lines, numbers, PBX, ISDN, broadband, fax machines, alarms, lift phones, PDQ terminals and migration concerns. VoIPTelco will help map the safest digital voice route.
- Audit PSTN, WLR, ISDN and analogue dependencies.
- Choose digital landline, VoIP, SIP, Teams or hybrid migration.
- Plan number porting and controlled cutover windows.
- Review broadband, power backup, failover and emergency continuity.