In 2025, BT will flick a switch and ISDN (Integrated Services Digital Network) telephony will be no more. Most businesses don’t follow the world of telephone systems closely enough to be aware that change is coming, and those that are aware might be looking at this date and thinking “Let’s put a pin in it and address that in the middle of 2024.” However, when you consider that the average telephone system serves a company for 9 years, that means that companies who are purchasing ISDN solutions today are already paying for something that will be obsolete before its life is complete. Can your business afford to purchase such fundamental resources knowing that 20% of the cost is straight to the black hole of unutilised expenses?

*By Steve Burnley – Collaboration Technical Lead

What is ISDN?

ISDN (Integrated Services Digital Network) is a set of communication standards, that allow simultaneous digital transmissions of voice, data and other network services, across the existing PSTN (Public Switched Telephone Network). When introduced ISDN allowed features that classic analogue phone networks couldn’t. It revolutionised the telecoms industry when it was first introduced, but now has become antiquated with the introduction of digital networks such as VoIP. ISDN lines can carry more than one user per line but are still limited to how many users can use a specific ISDN line. For example and ISDN2 line can only carry two users, and if you wished to have four, you’d need to install a send ISDN line, rather than just plug two more phones into your system like you could with VoIP.

Below we’ll show you not only the pros and cons of each system, but highlight how their implementation could be affecting your business, especially when it comes to efficiency and costs.

What is VoIP?

Simply put, VoIP (Voice over Internet Protocol) is a phone service that uses the internet. Through this system you can make calls using your internet connection, with network and geographical boundaries being almost non-existent. As this is a digital platform, various features that were either really expensive, or impossible to implement in the past, are now able to be implemented. These features include: conference bridges, voicemail, IVR (Interactive Voice Response), call diverts, voicemails that can be sent to emails, call recording, time of day rules, ring groups… As you can see VoIP is incredibly customisable. Currently, its largest user-base is home consumers and mobiles users, but 30% of VoIP users are businesses and this is the fastest growing user-group. Obviously a VoIP network is much more complicated than just plugging a phone into an internet connection, but we ensure that the hard work is done for you. You don’t have to be a VoIP expert to use a VoIP system, we can handle everything for you.

One of the key factors that makes VoIP so appealing as a system for business calls (as opposed to ISDN) is its flexibility and cost effectiveness.

ISDN Reliability

No simple initial setup, and if the system fails it goes completely, unless there is a whole secondary system in place. System maintenance is usually covered by an internal IT department or outsourced to a maintenance contractor causing significant delays and business impact should the system fail.

VoIP Reliability

Altering the system takes seconds rather than hours. Diverting a call happens instantly, so contact is never lost. It can be used as either a primary or secondary solution. Multi failover servers located nationally and if you have more than 1 dedicated feed into your business VoIP is 99.99% reliable.

ISDN Flexibility

Once setup is complete, it is permanent and tied to ongoing contracts. Changes can take weeks, or even months. Tied to geographical area codes.

VoIP Flexibility

Scaling up and altering the setup is quick and simple. Changes can be made instantly. You are not tied to geographical locations anymore, thanks to virtual numbers. If you are a small business and a move is on the cards, the system comes with you with minimal disruption and minimal cost.


Very expensive to implement and call costs are considerably more than VoIP. Installing a single ISDN line could cost upwards of £150 just for the line (not including the call rates or line rental)

VoIP Cost

Installation and call costs are considerably cheaper than traditional systems. Some reports show that local call costs could be up to 40% cheaper and international calls can be up to 90% cheaper, compared to ISDN.

Simply put VoIP is the future. Catering for 1 seat SOHO (small office home office) SME (small to medium enterprises) and upwards.

If you need consultation on migrating to a VoIP system, contact fixmyline for further details.

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