The Demise of Landlines - ISDN Switch Off By 2025. What Next?

BT announced in 2015 that longstanding ISDN and portions of their PSTN network are to be switched off in 2025 and ISDN should be considered end-of-life by as soon as 2020, meaning that new packages for ISDN services won’t be available for purchase. As these have been the dominant method of telephony communication for a number of years now, this is a huge change that will impact businesses and people all over the UK.

By Suzanne Whetton

BT ISDN switch off date.

With the proposed plans, BT plans to migrate all relevant services to use VoIP - Voice over Internet Protocol - as the method of communication. But what does this mean for your business? What are the differences between each method and the reasons for making this decision? We start by defining ISDN, PSTN and VoIP, and then delve into the specifics of the PSTN and ISDN phase-out in the United Kingdom by BT, all whilst answering the most important question - ‘do I need a landline anymore?’

BT ISDN Switch Off

PSTN (Public Switched Telephone Network)

This is the oldest of the three services, with historical roots dating back to the 19th century. This network is a worldwide aggregation of the numerous localised networks that have been created over time and uses switching centres to connect the various networks together.

Whilst this began as an analogue platform, it has now been nearly entirely converted to a digital technology, as a means to support the growing demands of telephony communication in modern society. Regardless, any technology that has been built around 100-year-old concepts is going to have some issues.

ISDN (Integrated Services Digital Network)

ISDN is, in many ways, an extension of the original PSTN technology. It serves as a method to transfer a wider gamut of digital information over traditional telephony networks, bringing with it a number of modern benefits that were otherwise unavailable.

Prior to the conceptualisation of the ISDN protocol, only voice was being transmitted. This method allows for voice and additional data to be simultaneously transmitted through the same network, improving voice quality and adding functions such as video calling, call forwarding, and so forth. Other technologies have since implemented many of the defining features of this network-type, rendering many of the advantages of an integrated services digital network moot.

VoIP (Voice over Internet Protocol)

Designed to utilise the vast public internet network, VoIP delivers voice and supporting data through this network in a functionally-similar manner to digital implementations of PSTN technologies.

There have been a number of iterations of this technology, which has altered the compatibility of VoIP with other networks, such as PSTN. Modern VoIP solutions are designed to function with any network, and have proven to be a cheaper alternative to traditional PBX packages. Furthermore, the ability to handle large volumes of unique data has created unified communication packages where an entire communication platform can be handled in a single system -instant messaging, phone calls, video conferences, screen sharing and more.

With each technology explained, we can now discuss why this shift is occurring and the impact it could have on your business.

Why The ISDN Switch Off?

With millions of businesses in the UK still relying on ISDN to power their telephony communications, it’s a huge decision from BT to end support for the platform. New ISDN services will cease to be sold in 2020, meaning businesses and homeowners will have to purchase a VoIP solution.

This is a tactical decision, as BT are currently maintaining numerous legacy networks, causing spiralling of costs and additional headaches to keep them running. By transitioning entirely to a VoIP solution, which has been steadily gaining traction, approval and market share over the past few years, costs will be reduced and better maintenance of the network can be prioritised.

What Will Happen To ISDN Connections?

The ISDN is set to be completely switched off by 2025, although there are still a huge number of businesses and personal lines using this legacy technology, so it remains to be seen what will happen to any existing connections.

It’s highly likely that BT will reach out to specific clients as the date looms to bring them over to a VoIP solution, potentially offering incentives to make the transition. If your business is still using a legacy solution, it’s worth investigating the process of switching to VoIP over PSTN or ISDN.

Skype For Business


So which is best for you? Even in 2019, it’s a difficult question to answer, as there are a number of factors that affect how each will work for you. There are important points to consider that will help inform your decision as ISDN approaches end-of-life.


  • Longstanding technology that has been refined over years
  • Robust network that works with legacy and modern systems


  • Set to be phased out by 2025 and will not be purchasable by 2020
  • Costly to implement and lacks the flexibility to support expansion

VoIP Pros

  • Modern, future-proof technology
  • Easily scalable with your business at a low cost
  • Can extend into a unified communications solution for a fully-managed platform

VoIP Cons

  • Reliant on a high-quality, stable broadband internet connection
  • May not be compatible with your current infrastructure, requiring additional investment

It’s important to analyse your current situation and make a decision about what will be the next best step for you. While we strongly believe in the power of a unified communications solution for your business, including the costs and working efficiencies that are provided in these systems.

What Next?

Right now, nothing changes if you’ve already got a setup in place. If you’re looking to make a change in your telephony communications, however, it won’t be long before the choice is made for you - there’s only a small amount of time left to actually choose one or the other.

Depending on your current business requirements, both are serviceable options, but the depreciation of ISDN as a service should be heavily considered, as you’ll be going through this process all over again in the near future. VoIP therefore, it pays to integrate your business operation with this new technology sooner rather than later.

How can unified communications from VIA help you?

Unifying all your communications into one managed system helps organisations in all sectors and sizes work more efficiently and save costs.

VIA UC gives you the most advanced unified communication platform available today. UC provides your organisation advanced telephony through your client of choice, including Microsoft Teams and Skype for Business.

Multiple platforms under one system

VIA UC brings together all your communication platforms into one efficient system, integrating:

VIA UC integrated features

Beat the BT ISDN switch off with VIA.

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