Liza Bazilevici creates content at PBX.IM focused on cloud telephony, VoIP systems, and contact center solutions. She makes complex topics easier to navigate, offering practical insights that help IT teams and business leaders understand and choose the right communication tools.
The PSTN switch off is the permanent retirement of the UK's copper telephone network, scheduled for 31 January 2027. It ends traditional analogue landlines and ISDN services, replacing them with internet-based voice (VoIP). Every business that still relies on a BT phone line, ISDN circuit, or any device connected to the copper network needs to migrate before that date or risk losing service entirely. The good news is that modern alternatives are more capable and often cheaper than what they replace. Platforms like PBX.IM, which provides hosted cloud PBX with UK virtual phone numbers, make the landline to VoIP transition straightforward for businesses of all sizes.
PSTN stands for Public Switched Telephone Network: the analogue copper-wire infrastructure that has carried voice calls across the UK since the 1800s.
Openreach is retiring it because the network is old, expensive to maintain, and physically incapable of carrying the bandwidth that modern digital services require. Keeping it running alongside newer fibre infrastructure makes no economic or operational sense, and BT has been open about the fact that it simply cannot support two parallel networks indefinitely.
It is worth being clear on the distinction between PSTN and ISDN. PSTN carries analogue voice. ISDN (Integrated Services Digital Network) runs digital channels over the same copper pairs and has long been the standard for multi-line business phone systems. Both technologies depend on the same physical copper infrastructure, which is why both are being retired at the same time on the same date.
Openreach owns the wholesale infrastructure. BT, along with around 600 other communications providers, sells services on top of it. That means the switch off affects customers across virtually every UK phone provider, not just those on BT directly.
Yes. The original Openreach PSTN shutdown date was December 2025. Ofcom and industry groups pushed for an extension after concerns about vulnerable users, particularly those relying on telecare devices and personal alarms that run over analogue lines. The deadline was moved to 31 January 2027 to give providers more time for safe, managed migrations.
No further extension is expected. Ofcom has been clear that this is the final date, and Openreach has been preparing the network accordingly. Businesses that treat the extended deadline as breathing room rather than an action window are taking a significant risk.
Any device or service that depends on a copper telephone line is affected. This includes more than most businesses realise on first assessment.
If a device has a phone socket, it needs assessing before 31 January 2027, when landlines will be phased out
The three main replacement technologies cover different business needs and starting points.
VoIP and hosted PBX deliver voice calls entirely over a broadband connection, using desk phones, softphone apps on laptops, or mobile apps. There is no on-site phone hardware beyond the handsets themselves. This is the right fit for most small and medium-sized businesses, particularly those that rent rather than own their phone system.
SIP trunking keeps an existing on-premises PBX in place but replaces the ISDN circuits that feed it with SIP channels over broadband. This is the sensible option for organisations that have recently invested in a capable on-site PBX and want to preserve that capital investment while still meeting the 2027 deadline.
UCaaS (Unified Communications as a Service) combines voice, video, instant messaging, and meetings in a single cloud platform. It goes further than a like-for-like line replacement and suits organisations that want to modernise collaboration more broadly alongside the network migration.
PBX.IM sits across all three of these categories, offering hosted cloud PBX, UK SIP trunking, Microsoft Teams Direct Routing, and local UK virtual phone numbers, all from a single platform with transparent pricing.
Moving from PSTN to VoIP is not technically complicated, but it does require planning. The businesses that run into problems are almost always those that underestimate the number of lines they have, discover a dependency too late, or leave number porting until the final weeks.
Your main replacement options
Step-by-step migration checklist
VoIP pricing varies depending on whether you go for a per-user hosted system or a SIP trunk arrangement.
Typical market ranges for UK businesses:
PBX.IM pricing is positioned to undercut most enterprise-tier providers while matching them on features. The platform offers flexible monthly plans with no long-term contracts, transparent per-channel pricing for SIP trunks, and free inbound UK virtual phone numbers on most plans. For a business migrating 10 users, the monthly cost with PBX.IM typically comes in well below the mid-range market rate.
Leaving migration until after 31 January 2027 is not a grey area. The consequences are concrete.
The businesses most exposed are those with complex estates: multiple sites, legacy alarm systems, lift lines, and ageing ISDN PBXs. These take longer to migrate than a simple broadband phone swap, and that time is running out.
PBX.IM is built specifically for businesses making exactly this move. The platform handles the full range of migration scenarios without requiring multiple providers or complex integration work.
Number porting is handled directly, with a clean process and support throughout to avoid the delays that come from porting errors.
UK virtual phone numbers are available across hundreds of area codes, so businesses can maintain local presence or set up new numbers without any physical line infrastructure.
UK SIP trunking gives businesses with an existing SIP-capable PBX a straightforward path to replace ISDN circuits, keeping the existing hardware in place.
Microsoft Teams Direct Routing connects Teams to the PSTN (or rather, to VoIP) so businesses running Teams for internal collaboration can also use it for external calls, without needing a separate phone system.
Pricing is flexible and monthly, with no long-term contract lock-in. Setup is fast enough that a small business can be live the same day, and the platform scales from a single number to enterprise deployments.
