ISDN and PSTN Switch Off – A Guide

ISDN and PSTN switch off in 2025

So, what does the switch-off mean for your business? And what do you need to do to prepare?

To help, we’ve put together a handy guide. It covers:

• What is PSTN?
• What is an ISDN line?
• Why is ISDN being switched off?
• What is the ISDN switch-off?
• What is replacing ISDN and what are my options?
• VoIp or SIP? Which should I switch to?
• When to switch over and how long does it take?
• How does the switch-off affect my business insurance?

What is PSTN?

PSTN stands for Public Switched Telephone Network. And what’s that, you ask?

Simply put, it’s a landline. The same, good, old-fashioned telephone system we’ve all been using for over a century. An invention patented by Alexander Graham Bell in 1876, it still uses the same system to transmit voices: a network of copper wires.

While some people now manage to get through the day without using PSTN at all, it’s still in use by many -- businesses included. That’s because it’s secure and reliable.

Even if there’s a power cut, a landline still works unless the phone line’s been damaged. And the only way you can listen in to a phone call is to physically access the line itself. (A process known as wiretapping, because of the copper wire.)  

What is ISDN?

ISDN stands for Integrated Services Digital Network. It was introduced in the UK by BT in 1986. Old analogue lines were replaced with digital ones allowing features that weren’t previously available with a classic telephone system.

ISDN allowed the transfer of voice and data over the same line. You could run fax machines, card readers, modems, and telephones on one line. What’s more, ISDN was faster than other call setups.

Nowadays the internet is always ‘on’. Back in the 90s, you had to dial up for access. It could be a slow and frustrating process.

Why is ISDN being switched off?

In short, because ISDN technology can no longer keep up. Technology is constantly evolving, bringing with it heightened demand for fast connections, increased data and bandwidth.

ISDN seems very slow compared to the broadband and internet connection speeds we’re all used to these days. And although improvements have been made to ISDN since 1986, it is now rather outdated.

Traditional ISDN lines offer little flexibility – tying your business to one location. For many firms, the move to hybrid and remote ways of working makes the more flexible and scalable cloud-based systems a more obvious choice.

Given the competition, in 2015, BT decided that continuing to improve the ISDN network made no financial sense. Instead, to meet growing demand, the company decided to focus its resources on newer technologies.

What is the ISDN and PSTN switch-off?

In 2015, BT announced they are switching off their ISDN and PSTN networks by 31^st December 2025. In an increasingly digital world, neither system can deliver the required volume or quality of data. Voice calls will be made over the internet instead. 

Yes, we mean everyone. Business and home. And it’s not just your phone services you need to think about. It’s everything else that currently uses the old phone network, all your non-voice services connected to PSTN or ISDN lines. Things like alarms, EPOS machines, door entry systems, CCTV, and faxes.

Landlines will still exist after the 2025 switch. You could still have a landline in your home, but the technology underpinning it will be different. You’ll plug your phone into your broadband router instead of a socket in the wall.

Your mobile acts as a backup, in case of power cuts. Unless you live in a remote area with poor signal quality. If that’s the case, you’d be better off with a separate battery-operated handset for emergencies.  

For business owners with multiple sites, multiple lines and different data needs, it’s a little more complicated. And you have various options.

What is replacing ISDN and what are my options?

ISDN is being replaced with an ‘IP network’. It’s an internet-based system that uses ‘Internet Protocol’ (IP) to send and receive messages between one or more computers. Basically, it makes calls via the internet, instead of copper wire.

As a business owner, you’ll need a phone system which will work on an IP network. You have two options: VoIP or SIP.

What is VoIP?

Voice over Internet Protocol (VoIP) is the technology that converts your voice into a digital signal. It allows you to make a call directly from a computer, a VoIP phone, or another data-driven device. Simply put, it's a phone service delivered over the internet.

What is SIP?

SIP stands for Session Initiation Protocol. It connects your business phone system (PBX) to the network via broadband, ethernet or a private circuit.  And it gives you more than voice-calling.

As well as your voice, SIP also allows the transmission of data. It means you can share files, send instant messages and multi-media, and have video conferencing sessions.

A ‘trunk’ is the name for a communication channel that runs between one point and another. One point, typically, is your PBX (business phone system).

A SIP trunk is a system that allows many people to access the network by sharing a set of lines. Think of it like a tree trunk with lots of branches coming from it. SIP trunks are easy to install, cheaper to use and give you greater flexibility over phone numbers.

VoIP or SIP? Which should I switch to?

The main difference between VoIP and SIP is that VoIP limits you to phone calls over the internet. A SIP trunk can send voice, text, and video. The thing is, it’s not a case of switching to one or the other.

SIP and VoIP are intertwined. SIP is the technology that supports VoIP. In other words, VoIP uses SIP to make calls. And just to make things more confusing, SIP is the most popular supporting technology, but it’s not the only one available.

To work out what’s best for your business, the first thing to decide is whether you need a voice-only system or one that offers you multi-media options.

VoIP is cost-effective and easy to install but limits you to voice calls.

SIP trunking gives you flexibility. You can send multi-media as well as make voice calls. And it’s scalable, so you can add lines and features when needed.

Business owners have five options:

• SIP: If you already have a phone system on your business premises, SIP is probably the best solution. It uses virtual phone lines rather than physical lines. And as most systems are compatible with SIP, you may not have to change yours. You can keep your phone numbers and add or remove lines. What’s more, if you temporarily relocate, you can take your phone lines with you.
  
  
• Hybrid phone system: This combines ISDN, Analogue, Digital and IP into a single, flexible phone system. With a hybrid system, you don’t have to make huge changes to your existing hardware. You can have some services hosted in the cloud and keep others at your business location(s). There’s no monthly subscription once you’ve paid for your hardware.
  
  
• Hosted phone system: Cheaper than an IP/Hybrid phone system because there are no upfront costs, a hosted system has a low monthly cost. Your host manages it, but you choose the settings and maintenance is included in your monthly subscription. If you need to move to another office, you just plug in your phone system. You can route mobile calls through it and if there’s a power outage, your calls can be instantly re-routed. You’re unlikely to need physical cabling, but you’ll need a good internet connection.
  
  
• IP phone system: You pay for the phone system or rent it. You manage it and choose where to host it -- your own server/on-premise/private cloud via a data centre). In a power cut, your calls are re-routed. It’s great for remote working as you can make calls from mobiles using your system and add/remove users. But like a hosted phone system, you’ll need a reliable internet connection.
• Keeping your ISDN lines: If your budget is tight, keeping your existing ISDN lines is an option. You could buy any additional lines you think you’ll need to carry you through the next couple of years and switch to an alternative system when you can afford it.

When to switch over and how long does it take?

Business owners need to keep two dates in mind:

• 1 September 2023: You’ll still be able to use your ISDN phones right up until the switch-off date. But from September 2023 you will no longer be able to buy additional ISDN phone lines.
  
  
• 31 December 2025: After 31 December 2025, if you haven’t sorted out an ISDN alternative, you’ll be forced to use a basic internet-based phone system. And that might not suit your business’s needs.

It makes sense to start researching your replacement options now. That way you can find the best fit for your business and won’t be risking disruptions.

Leave it too late and you could find yourself with a phone system that doesn’t work for you. Or waiting for a replacement at the end of a long queue.

How long does it take to migrate your phone system? It varies from provider to provider and depends on how many sites your business has. But it can take as little as three weeks.

What does the switch-off have to do with my business insurance?

Do you have an alarm at your business premises? Does it alert a third party if triggered? (A call centre, for example, or the police.) And, importantly, is it a single path alarm or a dual path system?

Many insurers require dual path systems as these provide added protection. A dual path alarm system has more than one connection to the UK communications network. Whereas a single path alarm has only one.

If yours is a single-path system, as copper lines are turned off and removed, your alarm may lose its connection to third-party services. That means no one will be alerted if your alarm is triggered. Not only will that leave your business premises exposed, but it can also make your insurance invalid.

Check your business premises insurance policy wording. Does your insurer insist your premises are alarmed? If so, is a single or dual path system required? Do they recommend a supplier?

Either way, given the limitations of a single-path system, you’ll want to upgrade your alarm ready for the switch-over. Speak to your current alarm provider to assess your options. And check out other suppliers of smart security systems to compare.

You might want to do this sooner rather than later too. Because although Openreach plans to complete the changeover by 2025, the new communications network may arrive earlier in your area.

Business insurance from Towergate

We offer tailored business insurance and trade specific policies to suit your needs so that you can pick and choose the cover and limits required for your business.

For more information visit our small business insurance page or call us on 0344 346 0409 to speak to a specialist adviser.

About the author

Alison Wild BCom (Hons), MAAT, ATT, Taxation Technician is a highly respected industry professional who has been working with and advising SMEs in areas including tax, pensions, insurance and marketing for over 25 years. She is a member of the Association of Accounting Technicians (AAT) and Association of Tax Technicians (AAT) and also has considerable experience as a residential landlord.