Friday, March 29, 2024

ISDN & PSTN Switch Off

ISDN & PSTN Switch Off

This is a quick 5 minute guide to the ISDN and PSTN switch off, updated for 2024.

Known as the ‘BT ISDN Switch Off’, this will be a huge shift in the way people make phone calls in the UK.

The official final switch off will happen in December 2025.

Just under 2 more years!

For business continuity, it is vital companies learn about it and make the necessary changes now.

So let’s take a look at what it is and what you need to do to prepare.

What is PSTN?

A Public Switched Telephone Network (PSTN) refers to a telecommunications network which allows subscribers at different sites to communicate by voice.

Introduced during the 1800s PSTN allows for information to be transmitted through a network of copper wires.

PSTN has been used by businesses as their primary method of transmitting phone calls and fax transmissions for several years.

What is an ISDN line?

ISDN stands for Integrated Services Digital Network.

It’s a group of communication standards that use digital transmission to make phone calls, video calls, transmit data and other network services over the circuits of the traditional PSTN (Public Switched Telephone Network).

In 1986, BT introduced ISDN in the UK.

It replaced old analogue landlines to digital lines, adding features that weren’t available with a classic telephone system.

What is the 2025 ISDN switch off?

BT announced back in 2015 they will shut off their ISDN and PSTN services completely by December 2025.

Neither of these technologies are capable of delivering the volume or quality of voice data needed in this increasingly digital world.

Voice calls in the future will be made over the internet.

This is often referred to as VoIP (Voice over Internet Protocol), which makes use of newer technologies such as fibre optic connectivity.

Why is ISDN being switched off?

Although ISDN has been improved a lot since 1986, the network has remained relatively unchanged and is now a little outdated.

Broadband internet connection speeds are a lot faster and at a higher level than ISDN.

In short, ISDN can no longer compete.

Traditional ISDN lines also offer little flexibility.

Businesses are tied to physical locations.

With the shift to cloud-based systems that are scalable and flexible for remote working, IP technology is a better choice to meet these demands.

In 2015, BT decided it didn’t make financial sense to keep making improvements to the ISDN network.


Well, BT can now focus their resources on up-to-date technology like VoIP, building services for the future, whilst meeting the growing demand from businesses.

Are you planning for the switch off in 2025?

We're offering free advice to all businesses to ensure they are prepared for this change in 2025. Get in touch today or give us a call on +44 (0)1603 431200.

What will replace ISDN?

There are two options that will replace ISDN, VoIP and SIP.

What is VoIP?

Voice over Internet Protocol (VoIP), also known as IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over IP networks.

With VoIP, analogue voice calls are converted into packets of data.

Packets travel like any other type of data, such as e-mail, over the public Internet and/or any private Internet Protocol (IP) network.

What is SIP?

Session Initiation Protocol (SIP) is a set of rules that are used in multimedia communications to initiate and terminate data transfer between different users.

It is the way you achieve a VoIP call.

SIP is the technology that creates, modifies, and terminates sessions with one or more parties in an IP network, whether a two-way call or a multi-party conference call.

What can I switch to?

Put simply:

Choose VoIP if you want to buy a whole new phone system when you make the switch from ISDN.

Or go with SIP if you want to keep your current system when you make the switch.

How to switch from ISDN to hosted VoIP

Choosing a hosted VoIP phone system is the best option for you, if you already have ISDN lines and don’t want to commit to a phone system on location.

Switching from ISDN to VoIP is very simple.

  • Discuss your business requirements and how many phone extensions you’ll need with us. If this number changes, we will add and remove as necessary.
  • We take care of the setup for you.

Two things you’ll need to consider:

  • Can your internet connection deliver VoIP?
  • Can your office phone system support VoIP?

Most new office phone systems support VoIP but if yours doesn’t, you’ll have to replace it with an IP phone system.

If your internet speed doesn’t have enough bandwidth to deliver voice and other features, you’ll need to upgrade it to one that does.

💡 Need a FREE IT consultationGet in touch.

How to switch from ISDN to SIP

As they use virtual phone lines rather than physical lines, SIP and SIP Trunks are a great on-premise solution for a phone system.

You can choose systems like 3CX and Direct Routing for Microsoft Teams when using a SIP Trunk.

Due to their flexibility, speed, quality and lower costs, SIP Trunks are becoming the most popular alternative to ISDN.

Are you keeping your phone numbers?

Before you switch off ISDN for good, you’ll need a plan to port your numbers.

Number porting is the process of moving your telephone number from one provider to another.

If your business uses location-specific phone numbers or if you want to keep all your existing numbers, it’s a good idea to do this.

We offer number porting as part of our service.

This process can take up to a few weeks depending on your porting agreement with your previous provider and the amount of numbers you want to port.

What are the benefits of switching?

Switching comes with many benefits which are listed below:


Cut your call charges, line rental and infrastructure costs dramatically.

Whatever you’re using right now, we are confident that switching will significantly cut your costs.

Fully Featured

A host of new capabilities that will transform the way you work.

There is a whole range of features that are either not available or just too expensive on landline systems.

Voicemail, conferencing, presence status, comprehensive exchange functions, switchboards, CRM integration, call on any device, and more.


Improve the speed and efficiencies of your calls when dealing with customers.

VoIP gives you total control over your calls. It allows you to deal with customer calls faster and better than ever before, and reveals how you’re performing and where you could improve.


Combine phone calls, emails, messaging, scheduling, staff status, apps and your CRM into one unified system.

You can finally bring voice calls into your digital world, where they belong.


Disaster recovery specifically designed to bounce back within minimum downtime and data loss.

Store regular ‘snapshots’ of all your data – once daily to backup all your call recordings and specific configurations.

If your system fails, simply restore the last usable snapshot and you’re back up and running – usually within an hour.


What do you need to consider before the ISDN & PSTN switch off?

When are you going to switch?

If you’ve already made the switch, well done you! 👏👏👏

If you haven’t, now would be an ideal time to consider the alternatives to ensure your business is prepared for the switch off.

Is your current phone system, IP compatible?

As ISDN will be replaced with IP, you need to look at whether your phone system is IP compatible.

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.

Switching to IP relies so heavily on the internet.

This means 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 line.

How long does it take to switch over?

The process can take a couple of weeks, but this will depend on the size of your business and existing infrastructure.

With our experience, we can make the process easier.

Taking care of the porting process, as well as working with you to make sure minimal disruption to your business activities at the time of the ISDN switch off.


We really hope you enjoyed our quick guide to the ISDN & PSTN Switch Off.

Now we’d like to hear from you:

Do you have any further questions about this topic?

Perhaps you need to prepare for this event?

Either way, let us know your thoughts.

Did you know?💡

We specialise in VoIP and SIP solutions.

We can help with advice, installations, migrations, support, backup solutions and anything else in between.

Get in touch today or give us a call on +44 (0)1603 431200.


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