ISDN Switch Off

BT announced the ISDN Switch Off which means they will be turning off Digital and PSTN networks in 2025.

2025/12/01 10:54:30

Have you prepared your business for the BT ISDN Switch Off?

In 2015, BT announced the ISDN Switch Off which means they will be turning off Digital and PSTN networks in 2025 as the maintenance and running of these networks are costly and severely out of date. Due to this, as of 2023 BT will no longer accept any new orders or amendments to services applicable to any existing ISDN products.

Although 2025 can still seem a long time away for the big ISDN switch off, the impending freeze on amendments to existing circuits next year certainly isn’t. In potentially very little time, businesses could be left urgently needing to make changes they hadn’t planned and budgeted for in regards to their communications.

Fibre to the Premises

What Is ISDN? And what is PSTN?

PSTN stands for Public Switched Telephone Network. With PSTN, analogue voice data flows over phone lines (copper wires), which are operated by your phone provider and historically support the key basic functions of most organisations like broadband, fax, alarms etc.

ISDN stands for Integrated Services Digital network. ISDN, for years, has been the backbone of business grade functions such as video conferencing, data transfer and direct dials. ISDN digital services enable users to make simultaneous phone calls by providing multiple channels per line and are seen to have been more ‘business grade’ than their PSTN counterparts.

Why is this Switch Off happening?

Technology has moved on; with the growth of cloud and hosted phone systems the old ISDN network is becoming obsolete. BT are aware of this and feel it is time to call time on the old technology. Much like the analogue TV switch off, and many other large systemic changes in technology infrastructure over the years it is a good thing and while it may seem worrying it is a step forward in terms of communications for businesses.

ISDN was launched by BT in 1986 which was part of a similar move to then move away from traditional landline technology. ISDN allowed both data and calls, so businesses were certainly keen to move across. It was also part of the very early growth of video conferencing and it offered the best internet speeds at the time. However, we now have cable modems, WAN and DSL connections and the good old ISDN is ready to be put out to pasture. From BTs point of view, it is very much about building a system for future needs and setting up business communications for the next 30+ years. BT have been investing in this new technology for some time and it would not be cost effective to maintain an old system as well as build up a newer one.

ISDN Switch Off 2025

What will replace ISDN?

Very simply; VoIP (Voice Over IP).  As mentioned above, BT have been investing heavily in this technology. The future of communications will not include copper wiring, it will all be done via your broadband connection. VoIP is faster, more flexible and more scalable.

What if we still have ISDN?

First of all, don’t panic! While most businesses in the UK have already migrated their communications to IP based solutions to take advantage of the significant benefits of an improved service at a lower cost, there are still a significant number of businesses that still need to make the switch to IP. You still have plenty of time to future proof your telephone systems before the ISDN switch off which won’t be until 2025. That being said, it is the perfect time to look at VoIP telephone systems, often called hosted phone systems. It is very sensible to plan for the ISDN switch off and make the move to VoIP now rather than risk the rush as the deadline draws closer.

There are also significant advantages of moving across to SIP Trunking or cloud-based phone systems including a higher quality of service and significant cost savings.

PSTN Switch Off

What is the risk of the ISDN Switch Off or WLR Withdrawal?

The ISDN Switch off affects more than just the ISDN it is also being labelled as (WLR) Wholesale Line Rental Withdrawal. WLR Withdrawal means that all the existing analogue lines will go by 2025 and all the existing services on those Analogue lines will need to be replaced by an IP version. Therefore, the risk to businesses could be significant if they leave it to the last minute to make the switch.

If businesses are unable to make amendments to their ISDN circuits from 2020 and are seeing a decreased level of support thereafter from Openreach either directly or indirectly this could lead to fixed features which don’t support the business’s evolving requirements, increased rentals and call charges and in the worst cases increased downtime during outages.

What are the alternative options to ISDN?

There are two options for businesses to consider which are explained below. Both utilise the latest VoIP (voice over Internet protocol) technology, each delivered slightly differently. With the ISDN switch off coming these are the two options available to businesses in order to future proof their telephone systems.

SIP Trunking

This is the direct, like for like upgrade to traditional ISDN lines as the new technology connects to a SIP enabled PBX via an Internet connection, and in most cases can be easily scalable up and down in a matter of minutes.

Line rentals are normally 50% of their ISDN counterparts and offer free calls to UK Local, National and Mobiles.

Cloud Phone Systems

This solution removes the need for line rentals like ISDN and SIP, with most Cloud solutions offered on a per user per month basis, giving each user the ability to make/receive a call providing the Internet connection can support this.

Like SIP, calls to UK Local, National and Mobile destinations are typically free of charge.

Is it easy to migrate to a non-ISDN phone system?

Yes, we are very experienced in moving businesses from an ISDN/PSTN phone systems over to Hosted and SIP phone systems. There are a number of variables depending on your exiting telephone system, but the migration is far easier than most businesses think, and we can manage everything. Obviously, continuity of service is critical for businesses in terms of having phone lines up and working for customers and clients, so we work with you to minimise disruption. Do not be put of preparing for the ISDN switch off now because you may be worried about migration.

What are the benefits?

ISDN Switch Off 2025


Potentially large savings – With the introduction of reduced line rentals and free calls to the most popular destinations called by businesses, annual telephony budgets can be cut and used in more beneficial areas to support customers and employees.

ISDN Switch Off 2025


Easy Installation – IP services can be run over any Internet access and are normally available within hours of ordering the service, meaning no more lengthy waits for BT Openreach engineers to physically connect you to the exchange.

IP Cloud Solution


Flexibility – IP technology allows you to take your numbers anywhere in the UK with an Internet connection, meaning they are no longer tied to the Openreach exchange area they are held. Also, you are able to keep your old phone number.

IP Cloud Solution

Increased Resiliency – For safeguarding purposes, businesses cannot afford to be ‘off the grid’ when there is an Internet or hardware
outage. IP technology can failover to backup connections or be diverted to another destination to mean the business is always contactable even in an outage.

ISDN Switch Off 2025

Fraud Protection – Businesses are prone to being targeted by fraud during holiday periods. Although IP technology is much more secure and difficult for fraudsters to successful tamper with, it can also be configured to automatically block outbound calls when a daily call spend is reached.

IP Cloud Solution

What is Cavendish doing now in order to help your business prepare for the ISDN Switch off and move to an IP Cloud Solution?

Cavendish offers:

  1. No upfront cost for the Cloud Phone System*
  2. Free set up and installation
  3. Free Polycom VVX411 handsets
  4. Keep your existing phone numbers
  5. Free local & national calls
  6. Free calls to UK mobiles (4 main mobile operators)
  7. Cavendish manage the switch over for you to include staff training

*Existing cabling infrastructure may need upgrading to support voice over IP (VoIP) which we can quote & provide as required

Fibre to the Premises

Is our Internet Speed enough for VoIP?

If you do not have fast enough broadband you may experience a low-quality call and some issues with calls dropping out. These days most businesses have suitable broadband speeds, it is recommended you need around 5Mbps download and 2Mbps Upload as a minimum. However, the speeds you need are more likely to be dependent on your usage. If you have a lot of calls from multiple phones, then you may need to consider speed. However, some businesses only have a few calls a day and may not need to worry. Our team are on hand to answer any questions about Broadband Speed and can also help with Business WiFi and Internet Solutions.

What do I do now?

Well the first thing to do is simply be aware that the ISDN switch off is coming and that it will affect your business. If you are still on ISDN, then you must make plans to move across. If you would like to move sooner rather than later, which we very much recommend, then get in touch with our team today and start making plans. We can walk you through the entire process and have you up and running on a fast, cost effective and highly flexible VoIP telephone system long before the switch off comes so you do not need to think about it again.

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