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The ISDN Switch Off

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Telecommunications suppliers have been talking about the ISDN switch off and moving to VoIP and SIP for a while, but a recent survey with 1,021 respondents found that 33% of SMEs were not aware of the switch off and a further 10% of SMEs say they are aware of the switch off, but do not know what to do next.

Infographic to explain the timeline of the ISDN Switch Off

In this guide, we explore:

✔️ ISDN Lines

✔️ The ISDN Switch Off

✔️ SIP & VoIP

✔️ Which phone system is right for your business

✔️ On-premise Telephone Systems

✔️ Cloud Telephone Systems

What are ISDN lines?

ISDN stands for Integrated Services Digital Network and ISDN lines utilise this network to provide a telephone service. These lines come in two types:

📞 ISDN2 lines are a digital telephone service which will provide your business with a voice solution. ISDN2 lines are usually connected to your business telephone system, coming in pairs of lines, with a 2-8 user capacity. This type of digital service allows the user to make a combination of calls, connect to the internet and receive fax messages.

📞 ISDN30 lines are pretty much the same as ISDN2 lines, but they allow a capacity of 8-30 users. ISDN30 is ideal for larger business generally with more than 10 employees. An ISDN30 solution can be adopted to link two or more office locations as well as provide employees with individual direct dial numbers (DDI).

What is the ISDN Switch off?

Though ISDN services have been serving businesses across the UK well for many years, the way in which we communicate has changed. Businesses, employees, and customers are more connected than ever and technology has evolved to meet the needs of this changing communication. With an ever-increasing reliance on cloud technology services, as well as flexible and remote working, ISDN Services are no longer suited to the way in which people and businesses need to communicate.

BT is switching off the PSTN and ISDN networks – starting with a cease of new supply by 2023 and moving to a full migration to IP before 2025. 

This switch-off could affect thousands of businesses in the near future. Traditional phone lines are an aging technology that is associated with high maintenance and running costs. Despite having been updated radically over the decades since they were introduced, traditional lines are still essentially the same in setup and design as the original phone lines of the 1900s. The way that businesses work is fundamentally different to the way they worked in the 1990s. Workers tend to work from multiple locations at different times of day and traditional telephone lines just aren’t set up to handle that level of flexibility.

While 2025 might seem a long way off, it’s important that your business makes an informed decision about when to switch away from ISDN – the alternatives to ISDN are already likely to be less expensive than ISDN, and moving sooner can save your business money as well as transform your business communications.

It’s also important to make an informed decision about when to switch away from ISDN as in 2023 you will no longer be able to order ISDN services and by 2025 you must have totally upgraded to IP telephony to avoid interruption to your business. If you leave it until 2025, prices may increase and switching will take longer as businesses rush to switch before the deadline.

What are SIP and VoIP?


VoIP stands for Voice over Internet Protocol. VoIP enables the end-user to make and receive calls over a broadband connection. VoIP is the latest telecommunications technology, offering businesses a more cost-effective way to make phone calls as well as having the functionality of a premium-grade telephone system.

VoIP operates like a traditional, digital, or analogue telephone line, but with the added benefit of being considerably cheaper and future proof. When making a call over the Internet, VoIP converts your voice into a digital signal and sends it to the person on the other end of the phone – instantaneously.

The great thing however, is the person on the other end of the phone doesn’t even need VoIP to accept the call. A VoIP phone system can contact people who are using any device, from smartphones to phone boxes, making it one of the most efficient and flexible telephone systems on the market.


SIP stands for Session Initiation Protocol. Without being too technical, SIP or SIP Trunking is essentially an internet telephone line, much like an ISDN or analogue line, however, calls are routed over the internet instead of over a traditional copper line.

Sounds similar to VoIP, right? So what’s the difference? SIP vs. VoIP isn’t necessarily a direct comparison – while VoIP is a term that can be used to describe any internet-based phone service, SIP is a communications protocol that is used for most types of VoIP deployments. So, VoIP is the type of telephony service and SIP is the method by which it is delivered.

Benefits of VoIP

✔️ Cost Savings – VoIP is generally less expensive than an ISDN set up. This is because with VOIP, businesses no longer have to worry about expensive line rental as the phone system relies on a broadband connection rather than traditional telephone lines. This can be increasingly beneficial for businesses such as call centres which make a lot of calls daily as well as calling international destinations.

✔️ Portability – As internet connectivity becomes increasingly more accessible VOIP handsets can be plugged in on the move, wherever an internet connection is available. Employees can work on the move –  be it at home, in hotel or at the airport. With this kind of portability, VOIP  means your business telephone system can be accessed as conveniently as email.

✔️ Scalability – The majority of businesses overtime experience continued growth. Unlike a traditional Telephone System, VOIP is not limited to the number of extensions or lines it may have. Extra handsets can be plugged into an internet connection anywhere, with little to no training. This takes away the added cost of hiring a qualified telephone engineer.

✔️ Greater Resilience – If your ISDN line develops a fault, your telecoms system will be offline until it is resolved. If your business is offline and you cannot take calls, you customers will go elsewhere. If the data circuit on which your SIP trunks operate goes down, restoring the phone system is a relatively simple matter. You company calls can be rerouted over another data connection, such as your company leased lines or mobile phone, until normal service can be resumed. Customers will not notice any difference between SIP installed, disaster recovery is quick and business continuity will resume efficiently, with business operations experiencing little impact.

✔️ Better Resource Utilisation – ISDN connections are comparatively wasteful. When the line is not being used for calls, the capacity goes unused. SIP trunking allows businesses to get more from their connection, allowing calls to share connections with internet traffic thereby obtaining the maximum benefit from the supplied bandwidth. With careful management, companies can consolidate their existing telecoms connection by using what they have more effectively.

Which phone system is right for my business?

Midshire Telecom can meet your business telephony requirements as we supply a comprehensive range of solutions. Our team of experts can determine your telephony needs and address these with the right telephone system for your business, at the right price. Whether you work on the move, are a small to medium-sized company, home worker or a large multi-office organisation. Our business telephone systems can help promote flexible working as well as improve productivity for your business.

We’ve outlined the two main types of telephone systems that use SIP and VoIP; on-premise telephone systems and hosted telephone systems.

☎️ On-Premise Telephone Systems

An on-premise telephone system can run over traditional telephone lines such as ISDN but is more commonly used with SIP trunks as the ISDN Switch Off approaches. As the name suggests, an on-premise telephone system is physically located on a business’ property.

Midshire Telecom primarily offers the NEC SL2100 for smaller businesses and the NEC SV9100 for larger companies.

☎️ Hosted Telephone Systems

A Hosted Telephone System, sometimes known as Hosted VoIP, is a Unified Communications solution that does not use a physical telephone system based on your business premises. Instead, the telephone system is hosted in the cloud and your employees use desk phones powered over your business broadband connection.

But desk phones aren’t the only way to utilise a hosted telephone system, you can also use the following devices:

✔️ Headsets 🎧

✔️ Mobile 📱

✔️ Desktop, Laptop & Tablet 🖥️

Our Cloud Hosted Phone System, HostX, provides you with all of the functionality of a traditional phone system but without the need for expensive upfront costs for installation or the ongoing costs for maintenance. The hosted telephone system has the added benefit of being operated and maintained by ourselves, which gives your business the opportunity to spend more time on what matters most – your customers.

Find out more about our hosted telephone system HostX

To conclude…

The ISDN Switch Off is quickly approaching and the time for businesses to act is now. Getting ahead of the switch off puts your business at a distinct advantage and switching now can save your business money.

If you’d like to know more about the ISDN Switch Off, the alternatives to ISDN and the telephone systems available to your business, contact us to speak to a telecommunications expert.