BT ISDN Switch Off, the Full ISDN Switch off Guide for Businesses

Learn more about this landmark telephony event that’s due to take place in 2025.

All You Need To Know About the BT ISDN Switch Off

As our lives change and our requirements become greater and more immediate, the need for legacy technology, and outdated systems, to be replaced, in order to keep up with our demands, has become more vital than ever. From the technology we use in our personal lives, be it smartphones, wearable technology such as watches, or even household appliances that use the internet to offer customers new features, right the way through to businesses who use networks, reliable internet connections, and a host of other modern technology to function on a daily basis.

This shift and change are happening everywhere but, in particular, it is going to become prominent across the telephone networks of the UK. Known as the ‘BT ISDN Switch Off’, this huge shift in the way people make phone calls will happen in 2025 and it is vital that, for business continuity, companies learn about it and make the necessary changes now to avoid having to play catch-up in a few years.

This switch shouldn’t be seen as a bad thing, for businesses in particular this switch from traditional phone systems to new internet-based telephone lines is going to be transformative and ensure that outdated technologies are no longer needed. As a result, they’ll be able to enjoy the benefits of high-speed communication that utilises broadband and takes advantage of the flexibility it offers teams and users.

Here at Prestige Telecom Group, we are driven to ensure that, over the next few years, the millions of businesses that operate in the UK are made aware of these new VoIP-style systems and the urgent need for them to work with business telecoms experts now, so they are ready for when the big switch off happens in 2025.

BT ISDN switch off guide for businesses

This drive has led us to create this page on our site which is a comprehensive look at this topic and aims to cover absolutely everything you could ever wish to know about the 2025 ISDN Switch Off, also known as the ‘BT Switch Off’ or ‘Copper Turn Off’. On this page, which is split into sections, you’ll find all sorts of information, from the history of ISDNs, right the way through to the reasons behind it, and what you need to do now to make a success of the ISDN lines switch. Once you’ve gone through this content, you’ll feel confident about what to do next which, we hope, will be to pick up the phone to our expert sales team here at Prestige Telecom Group to talk about our business telecom solutions, business mobile broadband internet connections, virtual landlines, and VoIP systems – all of which can help you migrate to a fully-hosted cloud system. To learn more, get in touch with us today on 01329 554 375, or email us at to discover how we can help.


The Only ISDN Switch Off Summary You'll Need To Read...

This page goes into incredible detail about the ISDN switch off which, as we mentioned, is due to take place in 2025. From specific dates that you need to keep in your diary, right the way through to a history of ISDNs, how we came to use them, and why we need to replace them – we really will cover it all. But, to kick things off we thought we’d provide you with a summary of the ISDN switch off so that you have all the important information needed immediately to hand. As always, if you have more questions, feel free to get in touch with us and we’ll happily talk you through this pretty significant telephony event. Now though, let’s take a look at the plans.

The great BT Switch Off, as it is colloquially called, began way back in 2015 when this national institution made an announcement that they would be effectively turning off ISDN (Integrated Service Digital Network) and PSTN (Public Switched Telephone Network) lines and switching to digital lines, or internet lines. This means that from 2025 onwards, people won’t make calls using these analogue lines and instead switch networks to new IP technology, and SIP technologies, that are faster, clearer, and come with a host of new features.

Why Are BT Switching Off ISDN, Anyway?

The reason behind the switch off is simple, but fundamental to the smooth running of the nation’s telephony network. Essentially, it is happening because technology has become such a huge part of everyone’s lives that the traditional copper network that is used to make and receive phone calls can’t keep up with faster, slicker alternatives. ISDN and PSTN copper lines were introduced way back in 1986. To date, that is over three decades ago and, while regular maintenance and upgrades to the physical lines have been made by BT, the pace at which IP phone systems have become more developed, popular, and cost-effective has meant that no matter how much telephone system maintenance occurs, this outdated landline technology could never have kept up. The announcement in 2015 was BT acknowledging this and pledging to increase its investment in replacement products, such as VoIP services, which run on fibre optic connections and provide a greater experience for users, especially businesses.

Who Is Set To Benefit From The Switch Off?

From a selfish point of view, BT now has an opportunity to save money over time because they only have to manage one platform that has advanced functionalities and will be used way into the future, which will help keep costs down as systems become more popular, and cheaper. They also don’t have to spend vast sums on maintenance or deal with the hassle of travelling the country fixing old landlines that aren’t up to scratch. For companies, this switch presents an opportunity to become a genuinely remote organisation that isn’t tied down to an on-premise telephony network. A key problem with these traditional phone lines is that they are fixed to certain areas meaning people had to use them to make phone calls. Now though, because of the explosion in internet usage, people no longer have to rely on physical phone lines and can use business mobiles to make mobile calls from wherever they are in the world. The switch means they can take advantage of VoIP, virtual landlines, and other fibre products that allow them to make telephone calls.

How Prestige Telecom Group's Solutions For Businesses Can Help

So, there is a relatively brief summary of the events that have taken place, however, for a more in-depth view, be sure to check out the rest of the page. Now, while knowing about the events is one thing, the other element that is just as important, if not more, is knowing what your business must do to avoid this switch becoming a problem.

After reading this page, the next logical step is to get in touch with Prestige Telecom Group. Operating in the business telecom world, offering business telecom solutions to companies of all sizes, we are ideally suited to offer you a hassle-free, no-nonsense approach that will ensure that your future business plans are secure when the switch off arrives. Our business connectivity experts can get under the skin of your business and discover which bespoke solutions would work best for you before going ahead and installing a selection of new services that mean you can make and receive phone calls, and access super-fast business broadband, no matter where you are. What follows is a brief description of our main services, those that relate most heavily to the 2025 BT Switch Off.


Standing for Voice over Internet Protocol, VoIP will soon be the default way people and businesses communicate. This type of phone system frees you from an on-premise phone system that restricts your ability to work outside of the same four walls. Rather than speaking to someone over a standard phone line, on public telephone networks, VoIP allows you to communicate verbally with people over an internet connection, on a cloud network. Virtual phone lines that are held over an internet protocol (IP) lead to clearer call quality regardless of geography, as well as a range of other features such as automatic call routing, and brand-specific on-hold music.

Virtual Landline

Another great solution, that frees you from the office, a virtual landline is a business telecoms solution that makes it look, to customers, like you have a normal landline. However, this ‘office number’, once dialled, automatically redirects to the mobile phone or internet-connected device of a person in the business who has been assigned to answer it. The great thing about a virtual landline is that it can be answered from anywhere in the world while still appearing as if you have an office number. With a virtual landline, you can rest easy knowing that your customers only ever have to dial, and/or remember, one number the next time they need to contact your business.

Business Mobiles

Supplying teams with business mobiles ensure they can always be reached by you or their colleagues no matter where they are during business hours. As we head toward the big switch in 2025, the reliance on business mobiles will become even greater as businesses move away from traditional channels of communication, such as regular landlines, to more disparate forms of communication – devices that can be found in your pocket, not your desk. It’s important to ensure business mobiles are prevalent so that employees aren’t relying on their own devices which may be old and feature out-of-date technology. Business mobiles ensure people are taking advantage of the latest tech and remaining professional when on the phone.

A Full History Of ISDN

So, we’ve established the main points surrounding the ISDN switch off but, because this is a comprehensive guide, we want to go beyond the basics and take a deep dive into this topic so that, as promised at the top of the page, this guide ends up covering “absolutely everything you could ever wish to know” about the big 2025 switch off! Therefore, this second section aims to look back at how the ISDN (standing for Integrated Services Digital Network) came to be across the world. We’ll examine when this communication network first came to the UK, how it helped companies with business communications and phone calls in general, and we’ll also look at what organisation runs it, as well as a wide range of other subtopics. 

To learn more, please read on and discover how we came to rely on ISDNs to make voice calls, or, if you wish to hear about how our cost-effective solutions can help you take advantage of VoIP features, for instance, so you’re ready for the big 2025 migration to digital transmission, then feel free to get in touch. Our team, based down south, as we mentioned, would be delighted to chat with you if you’re looking to the future, and are ready to harness new phone systems and technology. Get in touch with us today on 01329 554 375, or email us at

What Is An ISDN?

The Integrated Digital Services Network (ISDN) is a system of telephone lines that helps create networks of communication that deliver data transmissions and high-quality voice calls. While many people think that ISDNs relate solely to traditional phone lines, they are used in a variety of other applications, for example, their continuous data transmission capabilities make them perfect for EPOS (Electric Point of Sale) machines, and intelligent tills. ISDNs were brought in to help people move away from traditional analogue lines (referred to as landlines by most people) to more sophisticated digital lines that sped up communications and offered clearer services.

A good example of an ISDN is a typical office phone system. Imagine you have a reception desk on a business site that has four or five different receptionists on the desk, taking calls at any one time. ISDN allows them all to use separate business telephones at the same time because they are all connected to different lines. The negative thing about this is that you have to install/connect new lines each time. This means your business scalability is hampered because installation takes longer. Think of ISDN like TV, before 2012, when television wasn’t digitised. Before the switch to Freeview, most people only had access to a handful of channels. Now, however, users can purchase a set-top box for a small fee and enjoy hundreds of channels for free. The ISDN Switch Off is the phone network’s equivalent. 


In the 1960s, as trade spread throughout the world, the analogue phone network could not handle the long-distance calls made by, for example, advertising executives in New York, who wanted to call their counterparts in the London office. Globalisation was continuing at pace and the then-current phone network was not able to keep up. It was during this decade, over 60 years ago, that the entire phone network began to change to a digital switching system. 

You’d think that the rest would be history and that the analogue phone line would be consigned to the history books. However, it wasn’t until two decades later, in 1988, that things started to progress. In that same year, the International Telecommunications Union (ITU), which was founded by the United Nations (UN), started to formally recommend to companies that they should invest in, and switch to, ISDN to communicate and sell their products.

The take up of it was slow, to begin with, and it wasn’t until the 1990s when big corporations, such as Motorola, offered ISDN channels to companies and people. This brought down global prices and made the ISDN channel the go-to phone service.

When were they first introduced to the UK?

The history of this particular telephone service in the UK begins in 1985. The ISDN was launched as a replacement technology on June 25th 1985 and was originally named Integrated Digital Access (IDA). The IDA was an extension of the digital phone network and allowed for much faster data transfer for customers and businesses. The IDA/ISDN was the only one like it in the world and BP (British Petroleum) were the first customers on this new network. 

This telephony event signalled the end of analogue phone systems. Originally, when these digital exchanges started occurring, the ‘last mile’, as it was termed, was done over an analogue system, between the customer and their local exchange. This led to the IDA being changed to the ISDN (Integrated Services Digital Network) because that term more accurately described the system that facilitated this new switch from analogue phone lines. 

As testing across the country became more widespread, ISDN was soon able to offer plenty of 64kbit/sec (kilobit per second) channels that both commercial and domestic customers could use. Because these were binary systems, as opposed to analogue, they were named ISDN B Channels. As business activity exploded, due to the invention of the internet, companies and organisations began to use this new network. From it, they could get some of the fastest internet access around (which in hindsight was extremely slow).

Who runs the ISDN?

The British Telecom Group, or as they are more commonly known, BT, run the ISDN network in the UK. They were the first people to announce that they had plans to switch off the network, and the Public Switch Telephone Network which ran it. This began with the announcement that they would cease supply in 2020, with the aim of undergoing a full migration in 2025.

The reason for the long wait is to ensure that everyone in the UK can transfer over to the internet provided network in good time. For businesses, they must assess their ISDN usage now so that they are well prepared, and can look forward to, the switch. The best thing to do is to invest in VoIP, SIP Trunks, and other business telecom solutions today. These solutions are what our team here at Prestige Telecom Group do best. They would be happy to help you adopt a hosted VoIP (Voice over IP) solution and digital telephone systems in time for this key date in 2025.

How Do ISDNs Work?

This broadband and phone service which, as we’ve mentioned, is being slowly phased out, can appear complicated and difficult to understand. So, to give you a better understanding of how this system works, and to emphasise how much better it will be when we are all using the new alternative solutions (i.e. the internet), we thought we’d explain how it operates.

In its most basic, fundamental form, an ISDN line is just a digital phone line. As a result, it’s not something you just plug into a telephone and expect to work. For it to operate, you need to connect it to devices that are ISDN-enabled – these are very often modems or telephones. The initial reason for using an ISDN channel was speed. A typical user could get either 64Kbps or 128Kbps from a Basic Rate ISDN. The reason for the two speeds was to allow for separate phone calls to be made and received at the same time. Several modems used Plain Old Telephone Service (POTS) lines that allowed you to plug into analogue devices and make several calls at once because each line could support this. 

Installing an ISDN channel is quite complicated and another reason why this classic product is being phased out. Once you had connected the modem to the computer, you would then have to programme it and tell it what phone numbers you want to use. Once that is done, you would then have to set it up to dial your internet service provider (ISP) which would give you a particular number that is configured for ISDN access. 

In summary, it’s all very complicated and it’s clear to see how VoIP solutions and other digital connections are preferred so heavily. With them, as we’ll explain in this guide, there is no complicated set-up or any process that involves ‘telling’ your modem which numbers to access. You simply download a piece of software and any device with a digital connection becomes a phone, with the ability to make a video call, as well as a broad range of other functions. This is one of the key benefits of VoIP, allowing business scalability to happen much faster and easier. 

What are the types of ISDNs?

Traditionally, there have been two types of ISDNs that have run on the Public Switch Telephone Network (PSTN). They are called the Basic Rate Interface (BRI), and the Primary Rate Interface (PRI). The BRI was the lower tier and provided users with an ISDN channel, and its basic features, for a low cost. PRI was the better ISDN channel and provided a much better, more reliable service, with faster speeds.

Contact Us To Learn More

As you’ll see on this page, we’re better equipped than most to help you take advantage of the upcoming changes to the way the country makes phone calls. There is still plenty of time to make the correct decision for your business and we would urge you not to rush into investing in equipment that may itself become obsolete in a year or two. The key to succeeding is a steady, well-thought-out plan, aided by the help of a business communication solutions team such as Prestige Telecom Group. Operating in Hampshire, we’ve had the pleasure of helping countless businesses with their telecom solutions in areas such as BournemouthSouthampton, and Portsmouth, as well as further afield in CardiffBirmingham, and Bristol. No matter where you, and no matter what your relationship is with your communication solutions, we can help. Get in touch with us today on 01329 554 375, or email us at

Have Questions?


Narrowband ISDN was an attempt to modernise the existing ISDN system by making it more digital, as opposed to its current analogue system. While well-intentioned, Narrowband Integrated Switch Digital Network (shortened to N-ISDN) did ultimately fail and become obsolete. It became so because it took far too long to agree upon a standardisation process, and, by the time it had been agreed, the technology that was initially put forward had become obsolete – a reminder of just how quick telephony solutions can change, improve, and adapt. The ‘narrowband’ refers to the use of communications, connections, and telecommunication tools across a narrower band of frequencies in any given communication channel, and is commonly used to carry voice data over a frequency set.

Known as an ISDN terminal adapter, it is a piece of technology that is used to stop a dial-up Integrated Services Digital Network line and instead connect it to a computer or LAN (Local Area Network). An ISDN adapter would be used by a business or consumer when they don’t have a dedicated ISDN telephone connection or sufficient computing equipment, they can sometimes be referred to as ISDN modems. The adapter transmits digital data directly from the computer to the specific ISDN line without having to switch between analogue and digital signals. This kind of equipment plugs directly into the serial port of your computer and acts like a modem.

Even in today’s world of superfast broadband, ISDN is still pretty quick. A typical line will run anything between 144 and 192 kbps (Kilobits Per Second), this can be increased by integers of 64kbps. It’s not that ISDN isn’t fast, it’s just the fact that broadband suppliers have advanced their technology to offer even quicker products, hence the ISDN Switch-off taking place in 2025. When it was first introduced, ISDN was the fastest connection solution out there and allowed businesses to take advantage of fast broadband, it surpassed dial-up and the more analogue rivals in no time at all.

An ISDN is an Integrated Services Digital Network that carries internet connectivity over specialist lines. A Digital Subscriber Line (DSL) is a connection that is ‘always-on’ and does not need to dial over the lines that it uses. The main difference between these two is that, with a DSL, a user can make calls while connected to the internet because the DSL does not need to dial out. This is unlike an ISDN, which does have to in order to create a connection and allow the data to flow through it. Another key difference is that DSLs use existing telephone lines and modems, whereas ISDN lines have to be installed and require adapters at both ends of the line. ISDNs must also be directly placed into the home business where it is being used.

Yes, ISDN, while being phased out and switched off in 2025, is still used today by plenty of people and businesses. ISDN is predominately used where broadband internet isn’t an option. Further, there are plenty of reasons why people choose to still use ISDN. For instance, it offers multiple digital services that operate through just one copper wire, it can connect devices and allow them to operate over one wire, and provides a higher data transfer rate. While plenty of providers and teams use it, time is ultimately going to see the use of ISDN end.

We use cookies to improve your experience on our site and offer you relevant information. Learn more