- Openreach plans to withdraw the analogue Public Switched Telephone Network (PSTN) and ISDN across the UK, with the national stop-sell already in place and the full switch-off targeted for 31 January 2027 (extended in some materials to end of 2027 for migration of remaining lines).
- Since September 2023 it has not been possible to buy new PSTN or ISDN lines on the Openreach network, so any new business line is already a digital service.
- After switch-off, voice services run over an internet connection using IP technology such as SIP trunking, hosted VoIP or a cloud PBX rather than copper phone lines.
- Ofcom rules give business and residential customers the right to keep their existing phone number when switching provider through number portability.
- Devices that rely on a dial tone, including some alarms, lift lines, payment terminals and door entry systems, may need replacing or reconfiguring before the line is migrated.
The UK is retiring traditional phone lines by the end of 2027. Businesses must move voice services to internet based options such as SIP trunking, hosted VoIP or a cloud PBX. Audit your lines and connected devices early and keep your numbers via portability.
Last reviewed: June 2026
What the PSTN switch-off actually means
The Public Switched Telephone Network, or PSTN, is the analogue copper telephone system that has carried UK voice calls for decades. Alongside it sits ISDN (Integrated Services Digital Network), the digital line technology many businesses adopted in the 1990s and 2000s for multiple channels and clearer calls. Openreach, the infrastructure arm that maintains most of the country's local phone lines, is retiring both. The copper voice platform is being switched off and replaced with services that carry calls as data over a broadband connection.
This is not a marketing exercise to sell upgrades. The underlying equipment in telephone exchanges is ageing, increasingly hard to maintain and reliant on parts that manufacturers no longer make. Rather than patch a network that was designed for a different era, the industry is moving voice onto Internet Protocol (IP), the same technology that already carries email, video calls and web traffic. For most businesses the change is invisible day to day once complete, because calls still ring, transfer and divert as before. The difference is what sits underneath.
The key date businesses need to plan around is the end of 2027. Openreach has confirmed a national programme to stop selling legacy lines and then withdraw them entirely. The stop-sell on new PSTN and ISDN products took effect in September 2023, meaning any genuinely new line ordered since then has been a digital service. The remaining task is migrating the millions of lines installed before that date. If your business still relies on an analogue line or an ISDN circuit, it will need to move before the platform is withdrawn.
Audit your telecoms estate before you migrate
The single most useful thing a business can do is build an accurate picture of what it currently has. Many organisations are surprised by how many lines and connected devices they are paying for, some of which have not been actively used in years. A clear audit prevents both overspending on replacements and the nasty surprise of a critical device going silent on switch-off day.
Start with the bills. Identify every line, channel and number on your current invoices, including any you cannot immediately account for. Then walk the premises. Look for anything that quietly uses a phone line rather than a person making calls: alarm and intruder systems, fire alarm monitoring, lift emergency telephones, CCTV connections, fax machines, door entry and access control, EPOS and card payment terminals, and any remote site connections. These are the devices most likely to fail silently because nobody is on the line to notice the dial tone has gone.
For each item, record the provider, the contract end date, the type of line, the numbers attached and whether the device depends on a constant dial tone. Mark anything safety critical, such as a lift line or alarm, as a priority for early attention. This inventory becomes the brief you hand to a new provider, and it is also the document that protects you if something is missed.
Your options after the switch-off
There is no single replacement for a copper line. Instead, businesses choose from a small family of IP voice services depending on their size, call volume and whether they already own phone hardware.
SIP trunking
SIP (Session Initiation Protocol) trunking connects an existing on-site telephone system, known as a PBX (Private Branch Exchange), to the public phone network over the internet instead of over physical ISDN lines. It suits businesses that have already invested in a capable PBX and want to keep it. A SIP trunk effectively replaces the ISDN circuit while leaving the handsets, call flows and internal numbering untouched. Calls travel as data, and the number of simultaneous calls (channels) can usually be scaled up or down far more flexibly than with fixed ISDN channels.
Hosted VoIP
Hosted VoIP (Voice over Internet Protocol) moves the entire phone system into a provider's data centre. There is no on-site PBX to maintain. Handsets, softphone apps on laptops and mobiles connect over the internet to the provider's platform, which handles call routing, voicemail, menus and diversions. This is often the simplest route for smaller businesses and those without existing phone hardware, because the provider manages the technology and you pay a per-user monthly fee.
Cloud PBX
A cloud PBX is closely related to hosted VoIP and the terms are often used interchangeably. The distinction is that a cloud PBX emphasises the full feature set of a traditional business phone system, such as call queues, hunt groups, auto-attendants, reporting and integration with customer software, delivered as a managed online service. For a growing business that wants advanced call handling without owning or maintaining a physical exchange, a cloud PBX provides those features on a subscription basis.
| Current setup | What it becomes | Action needed | Deadline |
|---|---|---|---|
| Single analogue PSTN line | Hosted VoIP number or digital voice line | Order replacement service, port number, check broadband | Before end of 2027 |
| ISDN2 or ISDN30 with on-site PBX | SIP trunk into the existing PBX | Confirm PBX is SIP-capable, install trunk, retire ISDN | Before end of 2027 |
| Older PBX not SIP-capable | Cloud PBX or hosted VoIP | Replace system, migrate users, retrain staff | Before end of 2027 |
| Alarm, lift line or payment terminal on a phone line | IP-enabled or mobile-connected device | Contact device supplier, upgrade or reconfigure | Before line migration date |
| Fax machine on a dedicated line | Email-to-fax or cloud fax service | Move to software service or retire if unused | Before end of 2027 |
Broadband matters more than ever
Because IP voice rides on your internet connection, the quality and resilience of that connection directly affects call quality. A business moving to VoIP or SIP should check it has enough bandwidth and, ideally, a reliable connection such as full fibre where available. Voice traffic is relatively light, but it is sensitive to delay and dropped packets, so a congested or unstable line will produce poor calls.
Resilience is the other consideration. With a traditional copper line, the phone often kept working during a local power cut because it drew power from the exchange. IP phones depend on local power and your router, so they stop in a power failure unless you add backup. Sensible mitigations include an uninterruptible power supply for critical equipment, a backup internet connection, or mobile diverts so that calls reach staff even if the primary line is down. Discuss continuity arrangements with any provider before you commit, particularly if your business cannot tolerate being uncontactable.
Keeping your numbers: portability and provider choice
One of the most common worries is losing an established business number that appears on signage, stationery and customer records. Ofcom rules require providers to support number portability, which means you have the right to take your existing geographic number with you when you switch supplier, including when you move from a copper line to a digital service. The losing provider cannot simply refuse, and the process is designed to keep your number live during the move.
When choosing a new provider, weigh the contract length, per-user or per-channel pricing, the support arrangements and how the migration itself will be handled. A provider that takes time to understand your audit, plans the cutover and tests connected devices is worth more than a slightly cheaper monthly headline. Read the small print on early termination and on what happens to your numbers if you later leave, so that portability remains protected throughout the relationship.
Building a migration plan
Treat the switch as a project rather than a single phone call. Once your audit is complete, sequence the work: deal with safety critical devices first, then core voice services, then secondary lines and legacy equipment that may simply be retired. Allow time to test, because real-world call flows, divert rules and out-of-hours routing often reveal gaps that look fine on paper. Brief your team so they know how to use new handsets or softphone apps, and confirm the cutover date in writing with your provider.
Starting early is the practical advantage. As the end of 2027 approaches, demand on installers and providers rises, and leaving a migration to the final months risks rushed work and limited availability. A business that plans calmly across several months can test thoroughly, keep its numbers, protect its alarms and lift lines, and move staff onto a modern system with minimal disruption.
Frequently Asked Questions
When is the PSTN switch-off?
Openreach is retiring the PSTN and ISDN networks, with the national stop-sell on new lines already in force since September 2023 and full withdrawal targeted for the end of 2027. Some areas migrate earlier under local programmes, so businesses should confirm the date that applies to their specific lines with their provider.
What is SIP trunking?
SIP trunking is a way of connecting an existing on-site phone system (PBX) to the public telephone network over the internet instead of over physical ISDN lines. It lets a business keep its current handsets and call flows while replacing the legacy circuit, and it usually allows the number of simultaneous calls to scale more flexibly than fixed ISDN channels.
Will my broadband be affected?
Your broadband becomes the foundation for voice once you move to IP telephony, so it matters more than before. Most modern connections cope easily with voice traffic, but you should check you have sufficient bandwidth and a stable connection, and consider a backup connection or power supply for resilience during outages.
What is a cloud PBX?
A cloud PBX is a full business phone system delivered as a managed online service from a provider's data centre rather than from hardware in your office. It provides features such as call queues, auto-attendants, hunt groups and reporting on a subscription basis, with handsets and apps connecting over the internet.
How do I migrate my business phone system before 2027?
Begin by auditing every line, number and connected device on your premises, paying close attention to alarms, lift lines and payment terminals. Choose between SIP trunking, hosted VoIP or a cloud PBX based on whether you keep existing hardware, confirm your broadband is adequate, arrange to port your numbers, and agree a tested cutover plan with your chosen provider well ahead of the deadline.
Can I keep my existing business phone number?
Yes. Ofcom rules require providers to support number portability, giving you the right to keep your existing geographic number when you switch supplier or move from a copper line to a digital service. Confirm the porting process and timescales with your new provider as part of the migration plan.
