What is the ISDN Switch-Off?

In 2015, Openreach unveiled plans to retire the business communication network commonly known as ISDN. The intention was to gracefully switch off all active connections in a phased approach, with the final circuit being terminated by 2025.

The programme is currently underway, with some areas already being migrated off the network. However, new orders are permitted until September 2023, where a forced migration will occur between April and December 2025.  

What is ISDN, and how does it affect your business?

ISDN Switch-Off - Collaboration

ISDN is an acronym for Integrated Services Digital Network. It’s a fixed-line communication service that can provide both voice and data to businesses over the same circuit. 

This allows businesses to generate a range of external telephone numbers for direct access to employees in addition to the main business number across the same ISDN connection.

The major benefit of ISDN is that it provides businesses with the flexibility to have multiple telephone numbers across a dedicated but limited number of channels.

When used for voice connectivity, ISDN is physically connected to your internal telephone system and programmed as an external line to allow numbers to be presented to your extension.

Businesses still using ISDN connectivity when their geographic area is due to be switched off will be forced to migrate to a new IP-based telephony platform or face disconnection. Those who have made the switch to VoIP Solutions have benefitted from the cost savings and improved functionality.

ISDN is available in two common variants


Also referred to as Basic Rate Interface, it is ideal for smaller businesses looking to take advantage of the efficiency of multiple numbers over a smaller circuit footprint. With the option to scale up as the business grows. Individual circuits consist of two channels for voice traffic and allow additional auxiliary channels to be procured in blocks of 2 to increase capacity.


Also referred to as Primary Rate Interface is provided for larger business customers with the capacity of up to 30 channels of service through a single circuit. Businesses can select how many channels they require based on the telephony demand and can choose any amount of channels from 8 to 30. 

There are an estimated 2 million ISDN channels in the UK, according to a study in 2018. The switch-off creates a compelling event for businesses to consider their options and next steps regarding their telephony services. 

Businesses still using ISDN connectivity when their geographic area is due to be switched off will be forced to migrate to a new IP-based telephony platform or face disconnection. Those who have made the switch to VoIP Solutions have benefitted from the cost savings and improved functionality.

Why is the ISDN Switch-Off happening?

ISDN Switch-Off - Krone Blocks

Technology is evolving at a significant rate. ISDN relies on an ageing copper network infrastructure, originally installed in 1986, which is starting to become difficult for Openreach to maintain. With newer and faster connectivity methods such as Fibre, superseding ISDN technology.

Over recent years, these newer connection methods have provided businesses with the platform to carry their voice calls over the internet, known as Voice over Internet Protocol (VoIP). VoIP provides a more flexible and cost-effective way for businesses to communicate.  

As such, it no longer makes sense for Openreach to invest further in its legacy ISDN network. By converting all services to IP, Openreach will be able to direct their resources and strategic focus into technologies that will allow them to meet future business demands within the UK. This means there will no longer be an available service for traditional fixed-line telephony users or fixed-analogue services in the coming years. Leading to traditional fixed lines and calls cease to exist.

How can you prepare for the ISDN Switch-Off?

First off, you should check whether you are currently using ISDN services for your voice and data connectivity. This should fairly simple to do by reviewing your most recent line rental bill.

If so, now is the right time to start exploring your options. There are several questions you need to consider before deciding what option is right for you:

  • What are my functionality requirements for today and the future?
  • How do I want my new services to support different working models?
  • Does my current PBX support SIP technology?
  • Are my current data circuits big enough to support a VoIP Solution?
  • When is my PBX maintenance up for renewal?
  • When are my ISDN Services up for renewal?
  • To help, we’ve broken down some of the solutions below; 

Move to a Cloud-based Telephony solution

Cloud-Based Telephony or Unified Communications is an innovative, flexible, and scalable set of business communication services hosted and managed in the cloud. Employees can share, message, video and call in one place, removing the need for multiple applications on the desktop. These services include the migration of your existing business telephone numbers onto the new platform, maintaining consistency of numbers whilst taking advantage of the added functionality.

Port existing number ranges to SIP

Session Initiated Protocol (SIP) is an IP-based protocol used to carry voice traffic over the internet. Existing numbers are ported from ISDN to SIP and presented as SIP trunks over the internet to an IP-based phone system. There are specific pre-requisites for connecting SIP trunks to an existing telephony solution, so it’s best to always seek professional help before making any decisions.   

Give Microsoft Teams a voice

Using technology known as ‘Direct Routing’, you can enable Microsoft Teams to make calls while retaining your existing provider utilising your lines and minutes. You can also sign up for a new provider if that suits you and your budget, as new providers can also be cost-efficient.

ISDN Switch-Off - Consultant

What are my next steps?

You should assess the possible options you have and start to formulate a response. Check the renewal dates on any contracts to help work out your timelines and plan accordingly.

If you are unsure of the right solution for your business, don’t worry; you still have time to decide before the ISDN Switch-Off. If you would like some helpful advice, please get in touch or complete the form in the link below for a free consultation. We will take the time to get to know your business and help you to choose the best solution to suit your needs.