PSTN and ISDN 2025 Switch Off – What You Need To Know

BT Openreach announced in 2015 that it will be switching off its PSTN and ISDN networks in 2025 in favour of IP voice services, with a gradual phase-out of the older systems. This marks the biggest change in the telecom industry in the last 30 years and leaves a lot of businesses wondering what their options are going forward.  

With BT stopping the acceptance of new orders for PSTN, ISDN2 and ISDN30 services from September 2023 and the gradual phase-out of ISDN having started this year, the time for businesses to act is pretty much hereWe’re revisiting the details of the switch-off and looking at what businesses need to be aware of when it comes to their current telephony solutions and switching to a new IP voice service. 

Firstly, let’s look at the technology that’s being phased out. 


What is ISDN and PSTN? 

The Public Switched Telephone Network (PSTN) is the landline telephone system originally set up for analogue voice communication. It works by sending analogue voice data over a circuit-switched phone line made of copper wires. Before digital transmission was available PSTN was the most reliable method of making voice calls and the main carrier for internet activity across the world.  

The Integrated Services Digital Network (ISDN) allows for the digital transmission of voice, video and other services simultaneously, using the traditional PSTN network. 


Why are they being phased out? 

Well, put simply both ISDN and PTSN technologies aren’t cut out for modern telecommunication. BT have recognised that IP telephony is the future of phone communications and with a lot of businesses already moving to these technologies the demand for legacy systems has dwindled over the last decade. Especially considering the setup and design is essentially that same as the original phone lines of the 1800s.


Will I be affected? 

Well if you are one of the two million businesses last reported by Ofcom to still be using an ISDN connection then yes you will! 

With the gradual switch off underway, it’s a good time to start looking at the options available to you and making sure you’re all set with a new system in good time. Don’t worry the alternatives have proven over recent years to be great options for any business moving from legacy systems. 



So, what are the options? 

When it comes to switching over to IP telephony solutions you have a couple of options, SIP Trunking or a Hosted Phone SystemBoth options allow you to make call over the internet but slightly differ in how they work and their setup. 

Session Initiation Protocol (SIP) Trunking allows you to make calls through your on-site internet connection via your on-site PBXWhen making a call, instead of calls going from your phone to the on-site PBX straight to the PSTN, they go from your PBX through your SIP trunk over your internet connection, with receiving calls coming in to your SIP Trunk, through the PBX to your phone. This meaning that you don’t have to rely on physical phone lines to make or receive calls. 

You can learn more about SIP Trunks and what they are here. 

With a Hosted Phone System or Hosted PBX you can switch your telephony system to a completely hosted cloud-based solution, meaning that you don’t require any physical hardware to make and receive calls or manage your system. By making calls over VoIP (Voice over Internet Protocol) all you need to do is plug your handset into your network and away you go. 

With a flexible system like this, you can manage and customise your telephony system via an easy to use platform, work anywhere with plug and play phones, softphones and applications as well as take advantage of a whole host of inclusive features that are often costly add-ons with legacy systems. 

You can read our blog on why you should consider moving to a VoIP system here. 


What do you need to consider? 

With the right partner, switching to an IP telephony system is straightforward, but we recommend a few things to properly consider before you make the switch. 


Your Existing System 

Dependant on how many users your business has you might already have some existing hardware that you use. If you are currently using a single ISDN line for one phone in a small shop, hairdressers or something similar, you’ll be best off switching to a fully hosted solution as it’s super low cost and flexible in case you want to add new users in the future or setup features such as call forwarding simply and easily. 

If you are a larger business with an on-site PBX, you might want to keep your existing equipment and adapt it to make it suitable for after the switch-off. In that case, it’s important that if you’re considering a SIP solution that your PBX supports IP telephony, otherwise it might not be worth the cost of putting a new on-site system in place to be compatible. In that case, you might want to consider a hosted solution to avoid the high upfront costs. 



When you’re switching to a system that relies heavily on your broadband connectivity it’s important that you’ve got something in place that can provide good speeds and is reliable. If you can afford it, it’s worth looking at taking a leased line which will give you guaranteed, uncontested speeds and service level agreements from your provider to ensure you always stay connected. 

We’ve written a blog to help businesses make the right choice for their connectivity, you can read that here. 


Number Porting 

If you are planning to switch system make sure that you put a plan in place to port your numbers over in good time. If you use location-specific phone numbers or if you want to keep all your existing numbers, you will have to port your numbers from your old provider to your new provider. 

This usually takes a few weeks depending on the amount of numbers you want to port across so make sure you mention this to your provider in good time, so you avoid any business disruption. 



With more and more businesses working flexibly with either full teams working from home or a mixture of home and office it’s worth considering whether you need a system that is easily transferrable between different locations. 

If that’s the case we strongly recommend using a hosted phone system which gives you the opportunity for staff to use the phone system from wherever they are based, whether that’s in the office as normal, taking a handset home to use or using their computer or phone as a softphone. 



Depending on how you utilise your current phone system you might have some requirements in terms of features that your system needs to have. Make sure you have a clear idea of what you’re looking for and to ask your provider what features are included and what’s available as a bolt-on. 

You don’t want to choose a new solution to then realise further down the line that it doesn’t have the functionality that you require. 


Need some extra help? 

The switch-off does provide a challenge for businesses who haven’t been considering moving their phone system to another technology so it’s completely normal to feel a bit overwhelmed or unsure of the best solution for your business. 

At Connexin we’ve been supporting business making the switch from legacy telephony to VoIP systems since 2006 so have helped countless businesses like your own put in solutions that fit for their teams. 

If you have any questions or queries our team of specialists are on hand to support you in making the best decision for you, no matter what that looks like. Fill in the form below and a member of our team will be in touch.