Should I choose an ISDN Phone Line?

ISDN (Integrated Service Digital Network) has been around for many years and has been considered the main solution for businesses when it comes to their communications.

It is a set of digital communication standards for the transmission of voice & data. It consists of physical copper and fibre optic lines connected via telephone exchanges across the world.

There are two types of ISDN phone lines – ISDN2 and ISDN30e.

  • ISDN30e services are more about providing high-performance voice services for business that need a minimum of 8 channels.
  • ISDN2 is similar to a standard phone line although with ISDN2 the lines can be used for phone and data calls.

Advantages of ISDN Phone Lines?

  • It has been a proven technology for many years and is very reliable when it comes to the quality of voice calls
  • It is still very flexible and can be incorporated into various systems.

Negatives of ISDN Phone Lines?

  • You are limited on phone numbers as they need to be geographical.
  • It can hinder growth plans as it does not easily expand to fit your business growth in terms of new users.
  • It can be costly if you do expand or move offices because of installation cost and also downtime would be an issue to overcome.
  • Limited options to keep inbound/outbound calls in service if ISDN circuit becomes unavailable
  • High rental costs for equipment
  • Some ISDN faults can take up to 72 hours to repair.

A Word of Caution: BT ISDN Switch Off

ISDN Phone lines are slowly being phased out; BT announced in 2015-16 that from 2020 you will no longer be able to purchase any additional ISDN lines. This has now changed and the new date is September 2023 before they withdraw the ability to purchase additional ISDN phone lines. Between April and December 2025, there will be a forced migration period before they switch them off.

This means you can still utilise ISDN phone lines until September 2023 but since it is out-dated technology, it is worth looking at alternatives, now, especially if you have plans to grow.

A number of years ago, something similar happened when SDSL was switched off.

We did our due diligence by telling our clients but one, in particular, did not respond to the urgency and on the day of the switch off, rang us up in a panic. Of course, we did get them up and running again, quickly but there is no denying there was downtime involved, so please don’t leave it until the last minute!

What if I already have ISDN Phone Lines in Place?

The key thing is not to panic, you do have until 2023 to purchase any additional lines, so as long as you purchase any phone lines you may need by then, you’d be fine for another few years.

Regardless of when you choose to make a change, it is still a good idea to think about your options are and plan it in, now. The good news is that if you do that now, it is a planned expenditure and not a surprise.

What are the Alternative Phone Solutions to ISDN?

There are two main alternatives:

Hosted Phone Systems

Hosted VoIP is cloud-based and best suited to small-medium sized businesses who are looking for the functionality and scalability of a phone system with no extra maintenance charges.

Each user has their own line and calls are routed via the internet.

Learn more about Hosted Phone Systems


SIP and SIP trunks are typically for an on-premise solution or a hosted telephone system that will use virtual phone lines rather than physical wires.

SIP is suited for larger businesses as it can prove to be more cost effective if there are a lot of users but there is a maintenance implication.

Learn more about SIP Lines

Compared to ISDN, both options are more flexible in terms of what telephone numbers you can have and the locations in which you can have them. They are quicker to install and offer a strong business continuity service that ensures your business never loses any calls.

+ - Is it easy to Migrate across to Hosted VoIP or SIP?

With the right provider (us) – yes. You’ll be able to port and retain your numbers over to SIP or a Hosted Phone System. The whole migration (depending on some factors like the number of sites) can take as little as 3 weeks.

Downtime is minimal whilst the numbers are migrated across.

+ - What do I need to consider with the Migration?

There are a few things you need to consider before you migrate; here are the general steps and some considerations you’ll need to make:

  1. Hosted VoIP or SIP?
  2. Plan the number of virtual lines required.
  3. Check the internet connection is able to handle this system
  4. Check that your current handsets are compatible with VoIP or SIP
  5. Phones will require configuration (physical handsets or softphones)

Continue your Research on the ISDN Switch-off

We have collated a selection of free resources, purely on the ISDN Switch-off. Topics covered include:

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Discover our Free ISDN Switch-off Resources