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the bt isdn switch off 2027

ISDN Switch Off 2025: Everything You Need to Know

With the integrated services digital network (ISDN) switch off date happening in January 2027, businesses must switch over to alternative communication methods with plenty of time to ensure a smooth transition. Here’s everything you need to know about the BT ISDN switch off and how to prepare for the switch.

What is ISDN?

The BT ISDN is a digital telephone service that transmits voice and data over a digital line. It’s provided reliable phone lines for office landlines and business phone systems since the ‘90s. The network has been widely used for voice and video calls, offering improved internal communications between remote offices and branches.

The data speeds of the BT ISDN network are very slow compared to modern broadband, which makes it an issue for modern businesses looking to scale operations and handle large volumes of data. Because of this, the network is ageing and the technology is becoming too expensive to maintain.

When is the ISDN switch off happening?

The original ISDN switch off 2025 date has been extended to January 2027. Businesses must migrate to alternative technology before the deadline, but we’re advising all business customers to move over to a fully digital service by 31st December 2026.

Stop-sell of ISDN Services has already been active since 2023, but the full phasing out takes a lot longer to ensure a steady process. This switchover marks the end of the traditional copper-based telephone network (PSTN) and the transition to alternative digital services like voice over internet protocol (VoIP).

How will the ISDN Switch Off affect my Business?

The closer we get to the ISDN switch off date, the British Telecom ISDN system may become more prone to faults, which can eventually cause you to lose your phone services. Missed calls and downtime can lead to lost sales and customers may receive a negative customer experience. This can damage your company’s reputation, leaving a lasting impression on your customers.

If you don’t move over to an alternative Business Phone System before the deadline, your services will no longer work. Businesses relying on ISDN for voice calls, phone systems or conference lines will lose service unless they upgrade.

It’s a good idea to switch over to a VoIP system before the ISDN Switch Off with plenty of time, to give your team enough breathing room to get used to the new system. Planning early will help with number porting, allowing your business to transfer a phone number to a cloud-based VoIP service before the 2027 UK deadline.

VoIP: The Replacement for ISDN Phone Lines

Voice over internet protocol (VoIP) is a modern technology that allows you to make phone calls over the internet, rather than through ISDN or PSTN methods. It does this by converting voice into digital signals and sending them over IP networks.

Switching over from BT ISDN to a VoIP system offers many benefits, including:

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  • Cost effective - These systems can lower call costs, especially for long-distance or international calls
  • Scalable - VoIP Phone Systems grow with your team and make it easy to add or remove users
  • Flexible – support remote working with seamless communication, no matter where your team are
  • Plug and play – easy setup means minimal hardware is needed for installation
  • Modern features – add ons available, such as voicemail-to-email, call recording and forwarding

VoIP is slightly different to session initiation protocol (SIP) trunking, which connects your existing phone system to the internet, without using the cloud. SIP trunking is ideal for those who want to modernise their phone system without replacing everything.

To prepare for the ISDN switch off date, small to mid-sized businesses should opt for VoIP Phone Systems. VoIP is also suitable for companies without existing phone infrastructure as it offers a seamless user experience, which is fully hosted by the provider.

How to transition from ISDN to VoIP

When moving over from ISDN to a VoIP system before the ISDN Switch Off Date, here’s the process to follow for a seamless rollout:

1. Assess existing telecom infrastructure

Consider your current setup, including BT ISDN lines, phone numbers, PBX system and connected devices. It’s a good idea to create an inventory or checklist and figure out what’s dependent on ISDN and what can be replaced.

2. Review call volumes and feature needs

To determine the right solution for your team, you need to take a detailed look at how your current phone systems are being used. Look into existing call volumes to see what VoIP package you’ll need to choose.

3. Choose the right solution

Next, you’re ready to sign up for a new solution; most users opt for VoIP or hosted PBX. Choose the right telecoms partner to work with you to ensure you select the right plan for your needs, and they’ll help you set up your new phone provider.

4. Schedule installation and porting

Most VoIP systems are plug-and-play, meaning installation is straightforward and hassle-free. These systems usually have a user-friendly dashboard to manage installation and settings. When you work with a trusted supplier like Birmingham Telecom, installation of the new system gives you one less thing to worry about when switching over.

To transfer your existing phone number from one service provider to another, porting can be done to prevent losing your number. This keeps everything running smoothly for your business, with no need to inform customers of a number change.

5. Train staff and deploy

Now you’re ready to roll out the new system within your company. A phased rollout is usually recommended to reduce disruption. It’s important to make sure each employee knows how to use the new system and all its features, such as transferring calls and setting up voicemails.

Why choose Birmingham Telecom for ISDN migration?

At Birmingham Telecom, we don’t just offer short-term solutions, we build lasting partnerships. With over 40,000 businesses supported and counting, we deliver trusted and tailored communication solutions that grow with your team.

Our experienced technical engineers and support staff speak your language, working closely with you to ensure a smooth BT ISDN to VoIP transition before the ISDN Switch Off Date. Whether you’re looking to scale solutions, onboard remote teams and new starters or just need ongoing maintenance support, we’re with you every step of the way.

Let us help you create a future-ready workforce with minimal business interruption and a phone system that scales with you.

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FAQs About the ISDN Switch Off

BT announced that the UK ISDN Switch Off and PSTN Switch Off will take place in two phases.

The first phase

This involves a “a stop sell” of new services and begins on 5th September 2023.

This stop sell prevents telephone providers from placing PSTN single line orders, PSTN multi line orders plus any order for  ISDN2, ISDN30 and ADSL, FTTC and G.Fast broadband products.

When this deadline is reached you will no longer be able to :-

  1. Transfer any legacy services “Like for Like” between suppliers (PSTN, ISDN ADSL or FTTC)
  2. Place an order to take over a working line Restart a phone line that is currently “stopped” ie. when you move into a new property with a phone socket on the wall
  3. Amend your ISDN DDI range
  4. Increase or decrease your ISDN channels
  5. Convert single analogue lines to multi lines or ISDN
  6. Amend select services on any phone line
  7. Add Broadband (ADSL and FTTC) to PSTN lines
  8. Migrate to non-ultrafast broadband products

The UK Switch off will affect business using either ISDN or PSTN technology.

Most commonly, the following services use either analogue or ISDN phone lines and need to be upgraded.

Analog telephone lines and voice calls made through PSTN or ISDN will be affected. Both businesses and residential customers will need to migrate to alternative voice services such as Voice over IP (VoIP) or digital telephony solutions.

Fax machines that rely on PSTN or ISDN connections for sending and receiving fax messages will need to be replaced or upgraded to digital alternatives.

Alarm systems that utilize PSTN or ISDN for monitoring and communication, such as burglar alarms or fire alarms, will require alternative methods of connectivity. Alarm system vendors should be contacted to explore options like cellular or internet-based monitoring.

Payment card machines that use PSTN or ISDN lines for transaction processing, such as point-of-sale (POS) terminals, may require migration to IP-based payment solutions or newer card readers that support IP connectivity or a mobile SIM.

Emergency services such as medical alert systems or emergency call points, may be affected by the PSTN switch off. If you use these services, please contact your providers as soon as possible to ensure continuity through alternative communication methods.

Electronic Point of Sale (EPOS) systems that rely on PSTN or ISDN connections for real-time transactions and reporting may need to transition to IP-based or wireless solutions to maintain functionality.

Lift emergency phones that operate on PSTN or ISDN networks will require migration to alternative communication technologies, ensuring uninterrupted access to emergency services.

Telecare services that use PSTN or ISDN for remote monitoring and support for elderly or vulnerable individuals may need to switch to alternative methods such as mobile or internet-based solutions.

Conference calling systems utilizing PSTN or ISDN lines for audio conferencing may require migration to VoIP-based conferencing solutions or online meeting platforms.

Some broadcast services, such as radio station phone-ins or call-in shows, that rely on PSTN or ISDN lines for live interactions with listeners may need to transition to digital platforms or VoIP-based call-in systems.

It’s important to note that your own specific service provider may already offer alternative solutions or guidelines.

If you need any help or need advice relating to any of these services, please contact us on 0121 716 8888.

The ISDN switch off is happening for several reasons.

One primary reason is the advancement and widespread adoption of digital communication technologies that offer better efficiency, flexibility, as well as being more cost effective for all involved.

Additionally, maintaining and supporting outdated ISDN infrastructure has become increasingly expensive for BT Openreach which makes this transition to digital voice necessary.

The ISDN switch off will require businesses to transition their ISDN phone services to alternative technologies.

This transition may involve upgrading to Voice over IP (VoIP) systems or a cloud based telephone system but ultimately, businesses will need to ensure compatibility, assess their needs and plan for the ISDN switch off to avoid disruption to their telephone services.

Whilst daunting when first thinking about the ISDN Switch off, migrating from ISDN to modern telephony offers several benefits and future proofs your business.

These benefits include significant cost saving, increased flexibility, improved homeworking capability, enhanced features (at no additional cost) as well as overall improved call quality and a better level of service from your provider.

Although the switch off is happening in December 2026, we highly recommend that you get a head start and switch over as soon as possible.

Businesses are now unable to order new PSTN or ISDN services following the “Stop Sell” in September of 2023 and therefore this could cause severe disruption to your business.

To prepare for the ISDN switch off, would would strongly recommend taking an early, staged approach when considering your options.  Whilst most small businesses can be migrated quickly, larger projects need planning and can take time.

Evaluate your current communication infrastructure and identify how ISDN is being used in your business.

Get advice on how alternative technologies such as VoIP, cloud hosted telephone system and digital telephony systems can help you.

Engage with a service provider like Birmingham Telecom in order to understand your migration options and timelines.
Plan the transition process, including assessing hardware and software requirements.

Ensure that your employees are trained on the new technology, the new systems and tools implemented.

Test the new solution and ensure compatibility with existing applications and services.

Implement an early, phased migration strategy to minimise disruption to your business.

Not necessarily,

In some cases you can keep existing phones if you use ATA adapters or SIP trunking to connect with the new VoIP system.

However, VoIP-specific phones offer more features like call waiting and caller ID, which may not be available on older models.

Generally, VoIP systems have cheaper running and setup costs than BT ISDN systems.

Since VoIP uses the internet for calls, there’s no need for dedicated phone lines, which can increase costs.

Long-term costs of using VoIP systems are generally cheaper and maintenance costs are lower.

Payment plans for VoIP systems usually take the form of a monthly subscription, with installation fees a potential add on.

Yes,

VoIP systems are considered a dependable communication method for individuals and businesses.

As long as the system has a proper setup and a stable internet connection, these cloud-based systems can be more reliable than traditional lines.

Emergency services and alarm systems that rely on ISDN connections will be impacted by the switch off.

Whilst it is rare we come across any business that uses ISDN for their alarm services, this is still a valid question and will likely impact some companies.

Most alarm providers are already aware of the impact the BT switch off will have and for years have already been working on alternative solutions to ensure the continuity of critical services.

If you feel like you could be affected, we would recommend that you contact the respective alarm system supplier to discuss your migration options and any necessary upgrades.

When upgrading from ISDN to VoIP, you’re able to keep your number through porting. This makes communication with customers remain seamless during the switch over.

In a nutshell, the ISDN Switch Off primarily impacts voice communication services rather than internet connectivity.

That said, there are still some businesses we come across that still use ISDN for data (their internet connection).  This is a legacy technology that offers extremely slow download speeds and it has been outdated now for many years.

Any business customer that is still using ISDN for data services should immediately assess their internet connectivity options and consider upgrading to full fibre or a dedicated leased line alongside their voice migration.

We find that in most cases, the transition from ISDN to digital voice is quick and simple (of course when handled correctly).

That said, we would recommend that you don’t overlook potential challenges you may face when migrating away from ISDN.  These include ensuring compatibility of new technologies with your existing infrastructure, training your team on the new systems and working with a partner who can handle the migration process without disruption to your day-to-day operations.

When you discuss the ISDN switch off with Birmingham Telecom, we always like to have a detailed discussion with you either over the phone or if possible, face-to-face which will allow us to get a feel for your work environment and how you currently use your existing legacy systems.

Absolutely.  We would strongly recommend that you at least consider your options sooner rather than later.  You should start planning and make the migration well in advance of the ISDN switch off date to avoid disruption later.

It is estimated that over 65% of small businesses are still not aware of the ISDN switch switch could lead to a huge influx of people trying to switch to digital voice closer to the switch off date.  If this happens there of course will be huge demand placed on BT Openreach who lay and install the infrastructure whilst service providers like ourselves will be swamped with orders which could cause delays! 

Yes!

We have already helped over 1,000 UK businesses with the PSTN and ISDN Switch Off.

Get your FREE PSTN Switch Off review and take the first step in ensuring you are ready for the big Switch Off.

Upgrade to VoIP before it’s too late

With the ISDN switch over date to VoIP Phone Systems happening in January 2027, it’s important to give yourself enough time to ensure the transition is as smooth as possible. We recommend all businesses make the switch by the end of December 2026 to prevent disruption and potential downtime.

Here at Birmingham Telecom, we’re here to guide you through the switch to help you set up the perfect new system for your business needs. Find out more how you Switch From Your ISDN and contact our team on 0121 716 8888 or email us on info@birminghamtelecom.co.uk.

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