In 2015, BT (British Telecoms) released an announcement declaring that, from 2025, ISDN (integrated services digital network) and PSTN (public switched telephone network) lines will be permanently turned off. Instead, every phone line in the UK will be digital, routing calls over IP (internet protocol). And, in the words of BT, “we mean everyone. Business and home.” Fortunately, the future-proofing process is already well underway in the UK, and cloud telephony infrastructure such as our VCC (virtual contact centre) can help ensure smooth business continuity.

But what does all this mean for UK businesses and their communications? What are the benefits of this new solution? How will you make and receive calls in the future, what are your options, and do you need to search for new technologies?

What is PSTN?

Firstly, it’s worth taking a look at PSTN and ISDN in a little more detail. A PSTN network (or public switched telephone network, to give its full title) is a classic or ‘rudimentary’ telephone communications system, allowing users in different locations to communicate by voice.

Tech Target refers to PSTN as “the world’s collection of interconnected voice-oriented public telephone networks;” essentially, “the traditional circuit-switched telephone network” (Tech Target).

The technology behind PSTN stretches all the way back to the 1800s, and relies on information and audio data transmitted through a system of copper wires. Many businesses over the years have depended on PSTN lines in order to carry out their operations: maintaining a supply chain, communicating with customers, providing services or networking prospects, for example.

What is an ISDN Line?

The ISDN network, or integrated services digital network, is a set of communication standards which use digital technologies to facilitate network services such as:

  • Telephone calls
  • Video calls or video conference calls
  • Data transmission

ISDN uses the traditional circuits of PSTN to make this happen. In the words of Techopedia, ISDN enables a “digital telephone connection and the transmission of voice and data over a digital line, and is a development of the plain old telephone service (POTS)” (Techopedia).

BT introduced ISDN to the UK in 1986, as a replacement of legacy telephone systems using traditional landline connections.

What is the 2025 ISDN Switch Off?

Back in 2015, BT Openreach announced that the UK’s PSTN (and ISDN) networks will switch off in 2025. You can think of this as a major step forward in something approaching a nationwide digital transformation; a phasing-out of legacy telephone systems, and the introduction of a telephony infrastructure that uses internet protocol and broadband connectivity.

Importantly, the ISDN switch-off is not limited to just telephones. It includes all devices that use the old phone network, and non-voice services connected to PSTN or ISDN, such as:

  • Security alarms
  • EPOS machines
  • Premises entry/exit systems
  • CCTV
  • Fax machines

The ISDN switch-off will usher-in a new era of telephony, one that leverages IP (internet protocol) systems. Businesses can get ahead of the ISDN switch-off by implementing forward-facing cloud telephony solutions, such as our VCC. This omnichannel and future-proof technology seamlessly enables VoIP (voice over internet protocol), webchat, social media, email and more in one centralised location. Get in touch now to learn more.

While PSTN is certainly historic, the benefits of IP (internet protocol) telephony are unarguable. All around us are significant updates in the way we communicate – think of smartphone apps, video conference sites, or the IoT (Internet of Things).

It’s the infrastructure behind our communications that needs updating, in order to keep pace; the telephone wires stretching across the countryside, the rubber-coated cables skirting around our doorways, or the 19th century copper wires running beneath our streets. They simply aren’t built to support this digital, internet revolution in communications.


Understandably, many businesses and users have a few questions about the ISDN switch-off. While “an essentially 20th century technology,” to quote BT Openreach, “PSTN has been the backbone of the UK’s phone network for decades.” Here are some of the most common questions we’ve encountered surrounding the ISDN switch-off, and the internet protocol phone system of the future.

Why is ISDN being switched off?

ISDN has come a long way since 1986. But the fact is, the ISDN system supports a communication system that, by now, has its best days behind it. To put it another way: phone calls that rely on copper wires are more than a little outdated.

The connection speeds afforded by broadband internet are significantly faster, more functional and capable of higher operational capacity than the classic ISDN network.

Offering little in the way of flexibility, and requiring businesses to be tied to a physical location, the ISDN network (itself reliant on PSTN lines) is no longer fit for purpose. As the world moves over to cloud-based solutions, IP technology is a far superior system.

What will replace ISDN?

There are two unified communications options businesses will have to consider after the ISDN switch-off: VoIP (voice over internet protocol) and SIP (session initiation protocol).

What is SIP?

SIP (or session initiated protocol) is a group of rules that initiate or suspend the transfer of data between users.

SIP trunks are the underlying technology that enable VoIP; creating, transforming and suspending data transfer within an IP network. That data transfer could be anything from a one-to-one voice call, to a video conference call with users in many separate locations.

What can I switch to?

Right now, SIP is the most popular solution to replace traditional phone lines, along with some soft-phones.

With that said, WebRTC is seeing increasing uptake – especially for browser-based systems and video conferencing tools such as Microsoft Teams and Slack. H.323, though, is itself relatively old, and has been superseded by SIP.

What is VoIP?

VoIP, sometimes referred to as IP telephony, is a grouping of technologies that facilitates the delivery of voice, data and video via an internet connection.

VoIP transforms analogue voice calls into a parcel of data which, like any other data, can be transmitted over the public or private (IP) internet.

Are there any concerns about switching to VoIP?

Moving to VoIP is, in this day and age, a vastly superior option; one which carries multiple benefits, as we’ll see in a moment. First, let’s touch on some of the concerns, or reservations, some users may raise:

  • Being locked-in to a long-term ISDN contract, and a reluctance to write-off that outlay. It’s worth knowing though that, even with early termination fees, it may still be cheaper over the next few years to make the switch.
  • The idea that ‘changing management = extra work’. While changing systems does of course require some effort, VoIP is actually remarkably easy to set up.
  • Limitations in connectivity; however, note that almost all modern broadband connections are more than sufficient to effectively support VoIP.
  • The attitude of ‘if it [ISDN] ain’t broke, don’t fix it’. In reality, ISDN will be completely obsolete very soon, so it’s a smart idea to get ahead of the switch.
  • Concern that VoIP won’t fit the company workflow. In fact, as ISDN becomes harder to maintain, VoIP allows you to implement a unified communication strategy.

So what are the benefits of moving to cloud telephony?

By switching to VoIP, you position your organisation to take advantage of numerous operational benefits, including:

  • 50-70% lower costs for calls. VoIP doesn’t necessitate any monthly line rental; moreover, you’ll be able to host video conferencing calls, forward calls between locations, use voicemail, implement an auto attendant – and much more besides – without the need to find extra budget.
  • No complex or costly hardware, or any related maintenance costs.
  • Simple functionality in routing calls.
  • A wide range of call features, supporting truly unified communications.
  • Massive scalability. In sharp contrast to hardware-based ISDN, VoIP is limitlessly scalable without the need for extra expenditure.
  • Enablement of homeworking or hybrid models. VoIP is remotely-operable, helping to keep your organisation connected, versatile and proactive.

How do I upgrade?

Modernising your organisation’s communications couldn’t be simpler, and you can make the move to VoIP as soon as you’re ready by following these simple steps.

  1. Find the right connectivity provider to support your journey.
  2. Take stock of your existing system and highlight opportunities to improve.
  3. Break down your strategy into short-term and long-term objectives.
  4. Execute the action plan step-by-step.

Navigating the ISDN & PSTN Switch Off Smoothly

Though the BT announcement came all the way back in 2015, businesses may be reluctant or slow to prepare for the ISDN switch-off. Nonetheless, there’s no getting around the fact that unified communications and integrated services are very much the future of telecoms infrastructure. Internet usage is on a turbo-charged upward trajectory, and IP calls along with it.

Over the next few years, we’ll see terms like ‘line rental’, ‘FTTC (fibre to the cabinet)’, ‘landline connection’ and ‘leased line’ take their place in telephony history. In their place, ‘cloud telephony’ and ‘full-fibre broadband connection’ will become commonplace. So, now is the perfect time to modernise your or business communications system, to get ahead of the ISDN switch-off and prepare your operations for the fast-incoming future of telephony.

Get your digital transformation in gear today. Implement a cloud-based virtual contact centre and ensure business continuity before, during and after the ISDN switch-off. Book a free demo today to take your organisation into the future of telephony communications.