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?

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more developed, popular, and cost-effective has meant that no matter how much telephone system maintenance occurs, this outdated landline technology could never have kept up.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. 

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 number 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.  

What Does My Business Need to Do?

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 Titanic Telecoms LTD, 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?

 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 Titanic Telecoms LTD about making the switch, we can ensure that the solution fits in with your plans. 

Is your chosen solution future proof? 

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. 

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 Titanic Telecoms LTD. Operating in Belfast, we’ve had the pleasure of helping countless businesses with their telecom solutions in all six local counties including the ROI as well as further afield in London, Birmingham, and more. 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 03303 200 222, or email support@titanictelecoms.com  

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