PSTN Switch-Off 2027: What UK Businesses Must Do Now

What Is the PSTN and Why Is It Being Switched Off?

The Public Switched Telephone Network (PSTN) is the UK's traditional circuit-switched telephone infrastructure — the copper wire network that has carried voice calls since the late 19th century. ISDN (Integrated Services Digital Network) is an earlier generation of digital telephone service that runs over the same infrastructure and is used by many businesses for multi-line telephone systems (PBX).

BT Openreach has committed to retiring both the PSTN and ISDN by 31 January 2027. The driver is straightforward: the infrastructure is ageing, expensive to maintain, and incompatible with the direction of modern communications technology. Carrying voice traffic over IP networks (the technology underlying VoIP and Microsoft Teams Calling) is significantly more efficient and flexible.

The switch-off does not affect the physical fibre cables Openreach has been laying — it affects only the legacy copper telephone network and the circuit-switched signalling systems that run on it.

Who Is Affected?

The switch-off will affect any business or individual that currently has:

• PSTN telephone lines: Standard analogue phone lines (also known as POTS — Plain Old Telephone Service) used for voice calls, fax, or as a secondary backup line.
• ISDN connections: ISDN2 or ISDN30 circuits typically connected to a business PBX system. These are widely used by businesses with on-premise phone systems and will cease to function entirely after January 2027.
• ADSL or FTTC broadband: Broadband delivered via the copper telephone network (ADSL, FTTC/VDSL) depends on the PSTN infrastructure. Many providers have already moved customers to SOGEA (Single Order Generic Ethernet Access), which does not require a telephone line, but some businesses remain on products that will be directly affected.
• Devices connected via telephone lines: This is a commonly overlooked category and includes:
  • Burglar alarms and fire alarms with PSTN diallers
  • CCTV systems with telephone-line monitoring connections
  • Card payment terminals using dial-up connections
  • Door entry systems with telephone line connections
  • Fax machines
  • Lift emergency phones

If you are unsure whether your business falls into any of these categories, the most reliable approach is to audit your current telephone and connectivity contracts and identify every service that references a telephone number or analogue line.

Timeline and What Has Already Happened

The PSTN switch-off has been a phased programme over several years:

• 2020: BT Openreach announced the January 2027 switch-off date and halted new ISDN product sales.
• 2023: Stop-sell on new PSTN and ISDN products — no new PSTN or ISDN orders accepted.
• 2023–2026: Active migration programme, with providers moving existing customers to IP-based alternatives. Some exchange areas have already been switched off as part of the early migration programme.
• September 2025: Openreach's published schedule shows several hundred exchange areas in active migration, with full national coverage by late 2026.
• 31 January 2027: PSTN and ISDN cease to function. All remaining connections will be terminated.

Businesses that have not migrated by January 2027 will lose telephony service entirely on that date. There is no extension, no fallback, and no grace period.

VoIP Migration: The Core Replacement Technology

Voice over Internet Protocol (VoIP) is the technology that carries telephone calls over an internet connection rather than a dedicated copper circuit. From the user's perspective, a well-implemented VoIP system is functionally indistinguishable from a traditional phone system — calls are made and received in the same way, telephone numbers are retained, and call quality is typically superior to ISDN when the internet connection is adequate.

How VoIP Works

Rather than using a dedicated circuit for each call, VoIP converts voice audio into data packets and transmits them over your internet connection. A hosted VoIP platform manages call routing, voicemail, call recording, hunt groups, and all the features previously provided by an on-premise PBX — but from a cloud platform, without on-premise hardware.

What You Need for VoIP

A successful VoIP deployment requires:

• Adequate internet bandwidth: Each simultaneous VoIP call requires approximately 100Kbps of bandwidth. A business with 20 users who might all be on a call at once needs at least 2Mbps dedicated to voice traffic. A leased line or high-quality full-fibre broadband is strongly recommended for businesses running VoIP at scale.
• Low latency: VoIP is sensitive to latency (delay) and jitter (variability in delay). Standard broadband with significant latency variation can cause audio quality issues. Quality of Service (QoS) configuration on your network router helps prioritise voice traffic.
• IP handsets or softphones: Physical desk phones can be replaced with IP handsets that connect to your network, or with software clients (softphones) on computers or mobile devices.
• A hosted VoIP platform: The cloud platform that manages your calls. AMVIA offers its own hosted VoIP platform as well as Microsoft Teams Calling (see below).

Number Portability

You can keep your existing telephone numbers when migrating to VoIP. The porting process typically takes 2–4 weeks and is managed by AMVIA on your behalf. Geographic numbers (01/02 numbers) and non-geographic numbers (03, 08 numbers) are all portable.

Microsoft Teams Calling

For businesses already using Microsoft 365, Microsoft Teams Calling is often the most natural migration path. Teams Calling replaces traditional telephony with a unified communications platform where users make and receive calls directly within the Teams application they already use for messaging and video.

How Teams Calling Works

There are two primary deployment models for Teams Calling:

• Microsoft Calling Plans: Microsoft provides the telephone numbers and call minutes directly, billed through your Microsoft 365 subscription. Simpler to administer but less flexible on call routing and generally more expensive per user than Direct Routing.
• Direct Routing: A third-party SIP provider (such as AMVIA) connects your Microsoft Teams environment to the public telephone network. This gives more flexibility on call handling, lower per-minute costs, and the ability to port existing numbers. AMVIA provides Direct Routing as part of its Teams Calling service.

Licensing Requirements

Teams Calling requires at least a Microsoft 365 Business Basic or equivalent licence, plus a Teams Phone licence (currently £7–£10 per user per month through Microsoft). Direct Routing does not require additional Microsoft calling plan spend. AMVIA handles licensing configuration as part of the Teams Calling deployment.

Is Teams Calling Right for Every Business?

Teams Calling works well for businesses where staff primarily work at desks or use laptops. It is less suitable for environments requiring physical reception handsets, complex multi-site call routing, or contact centre functionality — though Microsoft is extending Teams' capabilities in these areas. AMVIA will recommend the most appropriate solution based on your specific requirements; not every business needs Teams Calling, and not every business is best served by it.

Connected Devices: The Overlooked Risk

One of the most frequently missed aspects of PSTN switch-off planning is the impact on devices that use telephone lines for connectivity rather than voice calls. These devices will fail silently when the PSTN goes off unless they have been upgraded or replaced.

Alarms and Monitoring Systems

Intruder alarms and fire alarms that use PSTN diallers to notify monitoring centres are common in UK business premises. The alarm system itself does not change — only the communications module that connects it to the monitoring centre. In most cases, the dialler module can be replaced with a 4G or IP communications module at relatively low cost. Your alarm maintenance company should handle this, but you may need to prompt them explicitly.

Card Payment Terminals

Older PDQ/card payment terminals that use dial-up connections are affected. Most modern terminals already use internet or 4G connections and will not be affected. Check with your payment provider if you are unsure about your terminal's connection method.

Lift Emergency Phones

Lifts are legally required to have an emergency communication system. Many older lifts use PSTN-connected emergency phones. Responsible building owners and managers need to ensure these are migrated before January 2027 — this is a legal compliance requirement, not just a convenience matter.

Fax Machines

Fax machines connected to analogue telephone lines will stop working. The replacement is typically a cloud fax service (sometimes called Fax over IP or FoIP) that receives faxes as email attachments. AMVIA can advise on appropriate solutions for businesses that still rely on fax for regulatory or client-facing reasons.

What to Do Now

The most important thing businesses can do is start planning now rather than waiting for a notice from their phone or broadband provider. Many providers will migrate customers automatically and with minimal notice — you will have a better outcome if you have already made an informed decision about your migration path.

Step 1: Audit Your Current Telephone and Connectivity Arrangements

Identify every telephone line, ISDN circuit, broadband service, and connected device in your business. Check your bills and contracts. Include any remote sites, warehouse or retail locations, and any lines that may have been installed and forgotten.

Step 2: Assess Your Internet Connectivity

VoIP requires reliable, low-latency internet connectivity. If your current broadband is marginal, a migration to VoIP on the same connection is likely to result in poor call quality. Addressing your connectivity upgrade and your telephony migration together, rather than sequentially, is more efficient and often more cost-effective.

Step 3: Choose Your Migration Path

The principal options are:

• Hosted VoIP with IP handsets — suitable for most SMEs with an existing phone system
• Microsoft Teams Calling — suitable for Microsoft 365 users who want to consolidate voice into Teams
• SIP trunking to an existing on-premise PBX — if you have a modern IP-capable PBX system that supports SIP, you may be able to connect it to AMVIA's SIP platform without replacing hardware

Step 4: Plan Connected Device Replacements

Contact your alarm company, lift maintenance provider, and any other suppliers responsible for devices using telephone lines. Establish what needs to be replaced or upgraded and agree a timeline.

Step 5: Manage Number Porting

Initiate number porting at least 4–6 weeks before your planned go-live date to allow for the porting process. AMVIA manages porting on your behalf and will schedule it to coincide with your cutover.

Costs and Potential Savings

PSTN switch-off is often an opportunity to reduce telephony costs, not just maintain them. ISDN circuits are expensive by modern standards — businesses paying £60–£100 per month for an ISDN30 circuit with 30 channels will typically find that an equivalent VoIP system with 30 simultaneous call capability costs significantly less per month once all-inclusive call bundles are factored in.

Indicative costs for a VoIP migration:

• IP handsets: £50–£150 per handset, depending on model and features. Many businesses opt for a mix of physical handsets and mobile softphone apps, reducing the handset count significantly.
• Hosted VoIP monthly cost: Typically £5–£15 per user per month, including calls to UK landlines and mobiles.
• Microsoft Teams Phone licence: Approximately £7–£10 per user per month (through Microsoft's licensing).
• Migration and setup: AMVIA includes configuration, number porting management, and user training within its standard VoIP deployment service. One-off project costs vary by complexity.

How AMVIA Can Help

AMVIA has managed PSTN and ISDN migrations for SMEs across the UK and understands both the technical requirements and the business change management involved. Our approach is to assess your current setup, recommend the right migration path for your specific circumstances, and manage the transition so it does not disrupt your operations.

We do not have a commercial preference for one solution over another — if Teams Calling is the right answer for your business, we will deploy it. If a standalone hosted VoIP platform serves your needs better, we will recommend that instead. Our interest is in a migration that works, not in selling the most expensive option.

Contact us to discuss your PSTN switch-off timeline. Early engagement gives you the most options and the lowest risk of disruption.