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What’s the difference between ISDN & VoIP?

Posted on 15 April 2021 by Beaming Support

You may have been made aware that ISDN telephone lines are being phased out and replaced with VoIP.

Why is this happening, why should you make to switch from ISDN to VoIP? Here we’ll compare VoIP technology with ISDN to help you understand why the change is happening, and what kind of technology you’d be best to choose when you’re looking for a new telephone system for your business.

At a glance: ISDN vs VoIP

Number simultaneous calls possibleUp to 30Limited only by your internet connection. A typical ‘Superfast’ broadband supports roughly 20 concurrent calls.
End of life date2025Unknown but it’s unlikely to be anytime soon.
Devices it can be used on·         Desk phone·         Desk phone

·         Mobile phone

·         Laptop

·         Desktop

Call qualityAverageHigh definition (with the right connectivity)
Keep phone number when moving location? Numbers can’t be ported with ISDN, but a divert can be set up, meaning you need to keep your old line.Your phone number is not attached to any physical location so it stays with you.

What is ISDN?

ISDN (Integrated Services Digital Network) is a fixed line service capable of delivering voice, video, data and more. It can be used to make multiple simultaneous phone calls, which are controlled by a PBX.


  • This is a tried and tested technology which has worked reliably for many years
  • Many businesses have used the same ISDN phone system for a long time, making it familiar and convenient for staff.


  • ISDN was introduced to the UK in the 1980s, and is not capable of delivering the volume or quality of voice data required by modern businesses.
  • ISDN will be switched off in 2025, making ISDN phone systems obsolete.


What is VoIP?

 VoIP is a broad term that refers to Voice Over IP – in other words, phone calls that are transmitted using the internet rather than a traditional phone line.


  • VoIP is also a tried and tested technology, it’s been around since the 1990s.
  • Predicting the future is tricky, but we’re willing to say that the internet is not just a passing craze. With ISDN lines being shut off, a VoIP system is the future-proof way to communicate.
  • There are many VoIP providers out there, and different types of system to suit your business. Do you prefer to host your own equipment or keep your phone system in the cloud? You can make a decision based on your business needs.
  • VoIP technology – and especially cloud-based VoIP – can be used on a familiar desk phone, but also on a computer or mobile phone, so you can work from anywhere. It’s also really easy to add or remove users and features can be enabled or disabled on a user-by-user basis.
  • Your phone number is yours. With VoIP, your phone number is not associated with any physical line, so it’s yours for life, even when you move to a new location.
  • Call quality. No more crackly lines, you can carry out calls in HD with VoIP.
  • Simultaneous calls. You won’t have to wait for anyone else to finish a call; the number of concurrent calls that can be conducted is limited only by your broadband or fibre connection.


  • Because calls will be made using your internet connection, it needs to be really reliable. Perhaps not a “con” so much as an opportunity to make sure you’re working with an ISP that prioritises the availability and stability of your connection.


ISDN vs VoIP: Which should I choose if I’m picking a new phone system?

 If you’re planning to wind down your business and retire in the coming months, you could perhaps stick with ISDN. In any other case, we’d strongly recommend that you make the switch to VoIP.

Although the deadline date of 2025 is still a little way off, you should start thinking about moving over to a digital phone line. If you’re thinking of eking out your old setup for a little while longer it’s worth bearing in mind that support for these older systems may wind down as the end-of-life date approaches.

Click here to read our post: What’s the best digital phone system for my business?

Should my business be worried about the UK ISDN switch off?

Enquire about BeamRing VoIP phones

Ready to find out more about making the move to VoIP? Use the form below to get in touch and one of our friendly team will be in touch within one working day to find out how we can help.


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What do BeamRing customers say about cloud based VoIP?

About Beaming

We are an Independent Internet Service Provider for UK businesses. Serious about service with a network built for business; we make sure you stay connected.

From the resilient and secure network we’ve built, to the choice of tailormade products all supplied with expert service, we provide peace of mind that businesses require.


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