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 03303 200 222, or email us at info@prestigetelecomgroup.co.uk.

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.

ISDN Switch Off: What Next?

When Does The Big Switch Off Happen?

BT has set the target date for the big switch off as 2025, with a forced migration phase between the months of April and December. From 2025, every phone line in the country will have switched from a PSTN/ISDN service to a fully digital service, routing calls over an IP (Internet Protocol). Whilst the 2025 date is considered the most significant, and a milestone in the switch off process, there are still dates to note beforehand. 

BT’s current plan is to cease the installation of ISDN lines nationally in 2023, but this may happen sooner in parts of the country that already have a high level of coverage thanks to gigabit-capable networks, which will be introduced from the summer of 2021 in certain areas. BT actually announced this switch in 2015, stating that from 2020, ISDN lines would no longer be available to purchase. They have since revised this date, and you can still purchase ISDN lines up until September 2023.

Whilst 2025 might seem like a while off yet, it’s important to be aware of the changes so that you can plan your move – there may be a lot that you need to do. For example, you’ll need to review everything that’s connected to your phone lines, such as alarms. If you haven’t already, it’s probably time to move to a digital-focused way of working, considering the cloud as an option for operating and communicating.

Why Is It Happening? What Are The Reasons?

When BT announced the switch off back in 2015, it acknowledged the evolution of technology and the need to move to digital. Technology is a huge part of our lives and the old copper network now struggles to keep up with this increased use of technology, as well as its evolution. Even since the announcement in 2015, technology has continued to evolve with the likes of Zoom, the cloud, and the numerous changes and improvements made to smartphones. This in itself exemplifies the need to switch to digital from ISDN.

The switch off isn’t happening just simply because the current phone system is old, although that is a key reason. The reasons extend far beyond the phone system to all digital communications in general. We now need more than these older technologies were designed to provide, and switching to IP provides the solution for individuals and businesses. It can also be incredibly cheaper to use, making it a no-brainer for businesses that want to get moving and make the switch before the 2025 deadline. 

The switch off then makes way for more efficient and effective products that will replace ISDN. This includes VoIP services which use a fibre optic connection and provides a greater user experience. Along with the announcement of the switch off, BT also announced it would increase the availability of these products to replace ISDN and, of course, many other providers will be following suit.

What Is It Being Replaced With?

When ISDN lines are switched off in 2025, they’ll be replaced with IP technology, which can be used in various forms. The most common forms of IP technology are VoIP (Voice over Internet Protocol) and SIP (Session Interface Protocol), but ultimately it’s down to you to decide what to replace your business ISDN lines with. 

There are several options available, all of which have their pros and cons – there will be a different ‘best option’ for every business, depending on your needs. Here are some of the replacement options:


These systems allow users to make normal calls to anyone, anywhere around the world, for a very low cost. VoIP stands for ‘Voice over Internet Protocol’, which essentially means that the user communicates with their voice over a broadband connection (this is the ‘IP’ part of the term, which means Internet Protocol). As such, a reliable internet connection is vital for VoIP to work. With no internet connection, there’s simply no phone system. If you choose to use this type of system, you’ll own the phone system and will decide where you host it.

However, with a stable internet connection, VoIP can offer numerous benefits to the businesses that make the switch. This includes greater flexibility and scalability – you can add and remove users as necessary and with ease, and you can work from anywhere because you’ll have the ability to make calls from your mobile using the system.

VoIP also offers a great degree of portability and is a cost-effective solution – VoIP is usually considerably cheaper than using ISDN lines. Better still, because the solution is often cloud-based, you won’t need to worry about maintenance costs. It’s worth noting though that you will also need to consider where to host your phone system- if this isn’t on-premise you may face additional costs and these should be factored into your considerations.


If your company has a compatible PBX (Public Branch Exchange), you may want to consider switching to SIP trunks, or SIP lines. This type of service is much more flexible and affordable compared to ISDN. SIP offers great flexibility when it comes to scalability – if you have a growing business or even plan on downsizing, SIP allows you to add and remove lines as necessary. As well as this, using a SIP trunking service allows you to reduce the amount of PBXs you need. Instead, you can keep your existing phone number, regardless of your location, meaning that if you decide to relocate, SIP will provide business continuity.

SIP also provides a high quality service for a lower price. SIP trunking has an underlying network quality that brings real benefits and value, yet this form of IP connectivity typically costs much less than using ISDN lines. 

Has It Been Done Elsewhere?

The move towards digital connectivity and communication isn’t exclusive to the UK – this shift is happening globally. Some countries have already switched off their ISDN and PSTN networks, with Estonia taking the lead, along with The Netherlands. Other countries have soon followed suit, with Germany, Japan and Sweden vowing to make the move away from ISDN and towards digital options – these countries are ahead of us and will make the switch before the UK.

Globally, telecommunications companies are realising that ISDN must now be replaced with more reliable options that can keep up with technological advancements and the customer behaviours that feed the demand for digital. As such, businesses across the globe are switching to digital, from analogue.

The Future: What Will Life After The Great BT ISDN Switch Off Look Like?

Even though the move might feel daunting, especially if you need to prepare for the switch, it should be a straightforward process and simply a case of changing your plan, package or provider. Once the switch off has happened and businesses have adapted to their replacement systems, they should soon start to reap the benefits of all-digital communications.

Following the switch off, no data will be carried through ISDN and PSTNs and phone lines will no longer require maintenance or recovery. Furthermore, IP and similar options can often be more cost-effective than ISDN, providing businesses with a much cheaper way of working. 

Not only this, but these systems can provide a greater degree of flexibility and scalability. With most of the digital systems, you can take and make calls from anywhere, on any device. You can also seamlessly integrate your business systems and apps with calls and video chat for collaboration and communication. With cloud-based systems, you can also access company work at any time, from any place. 

What Does My Business Need To Do Ahead of the ISDN Switch Off?

Things To Consider Before The ISDN Switch Off

Before the big ISDN switch off, there are a few things you’ll need to consider, to ensure that it doesn’t affect the way your business operates. 

Here are a few points to consider:

  • When are you going to switch? If you’re coming to the end of a contract for ISDN, now would be a good time to consider the alternatives, such as Prestige Telecom Group, to futureproof your business and prepare for the switch off. Even if you have some time left on your contract, it’s worth talking to a provider about how you can migrate to a different system.
  • How are you going to move forward with VoIP? Here, you need to consider your plans for the future and how your chosen solution needs to fit in with this. For example, if you have staff working remotely, or future plans to expand across multiple sites, then this can affect the package and the solution that you select. When you contact us here at Prestige about making the switch, we can ensure that the solution fits in with your plans.
  • Will your chosen solution work well into the future? The ISDN switch off is taking place because of newer, better technologies that can withstand demand. That’s a big sign that technology is always evolving as our demands increase. As such, you must ensure that your chosen replacement will be suitable for years to come, with high levels of flexibility and adaptability.

What You Need To Do To Prepare

To prepare for the ISDN switch off, you need to consider which replacement is best for your business, using the information that has been provided on this page regarding the various options and the things to think about. However, what’s just as important is when you prepare for the switch off. Because it’s expected to happen in 2025, putting alternative technologies in place might not feel urgent but, in reality, 2025 will be here sooner than you think. 

Aside from the switch off, there’s really no need to wait until 2025 to make a change – if you are using ISDN/PSTN lines within your business, you should consider your alternatives as soon as possible. Not only does this ensure that you’re prepared, but it means you can start benefiting from IP as soon as possible.

The process of switching will usually take a couple of weeks, but this can differ business to business depending on the infrastructure that’s currently in place. If you have multiple sites for example, the switch may take longer. By acting now, you avoid leaving things until the last minute and can take advantage of the solutions much sooner than 2025.

Does Your Current Business Telecoms Support This Change?

Because ISDN will be replaced with IP, you need to look at whether your phone system is IP compatible and can therefore support the change to IP from ISDN. If it isn’t compatible, then you need to invest in a newer model that is IP compatible. If it is compatible, then you may wish to consider replacing your existing ISDN service with SIP trunking, which is a flexible and cost-effective solution.

Regardless of compatibility, you may also want to think about using a cloud-based system for your business telecommunications – this is easy to implement for all businesses. As a software based solution, you can save money as you won’t need to purchase hardware or pay for the maintenance of the system and its servers. Instead, a cloud system is always up-to-date and provides all the useful features you’d have access to with a phone system that’s on-premise.

Because a switch to IP relies so heavily on the internet, you’ll also need to assess whether your internet connection is stable enough to support IP telecoms technology. If your internet connection needs upgrading, it might be time to switch to a fibre optic connection or ethernet-based leased lines, in the case of larger offices.

Should I Talk To A Business Telecoms Expert?

If you’re still unsure about what the ISDN switch off entails, what it means for your business, and what you need to do to ensure business continuity, then we’d definitely recommend speaking to one of our business telecoms experts here at Prestige Telecoms. 

Not only can we provide support and advice, but we can take you through the alternatives to ISDN/PSTN lines to find the best solution for your business. It’s important that you select a solution that isn’t just effective now, but also far into the future as technology continues to evolve at pace – our experts are best placed to help you make these key decisions. Then, once we’ve established the best course of action, we can handle everything including the porting process, to ensure that you experience minimal disruption to your day-to-day business operations.

To migrate to a better, more modern system than ISDN, get in touch with the team here at Prestige Telecom Group to ensure that you’re fully-prepared for the switch off. Call us on 03303 200 222, or email us at info@prestigetelecomgroup.co.uk

Benefits: How Will It Affect Your Business?

Whilst making the initial switch from ISDN to VoIP might feel stressful because of the considerations that you need to make, it doesn’t have to be. With our support, we’ll help you to switch to a better solution. Then, you can start reaping the benefits of IP. Here are just some of the advantages that IP offers:

  • It’s cost effective – VoIP is a low cost solution when compared to a traditional phone system. By eliminating the need for phone lines, this can reduce your costs.
  • It offers high quality – VoIP offers better audio quality and clarity, providing that you have a stable internet connection.
  • It’s flexible and scalable – VoIP can be tailored to your business requirements and can be adjusted if you downsize or grow in the future.
  • It’s portable – VoIP allows businesses to be as mobile as they need. Both desk-based and mobile users can connect to the phone system, regardless of where they’re based.
  • It’s futureproof – Investing in VoIP means investing in a modern phone system that doesn’t risk becoming quickly outdated. VoIP will be one of the main solutions for the foreseeable future.