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How to turn BT’s big ISDN switch off to your advantage

Ian Cooper, Head of Unified Comms Products at O2 explains how companies can switch from their legacy voice network to alternative advanced Unified Communication services.

As you will almost certainly be aware, BT plans to switch off its legacy voice network in 2025, and will not be accepting new orders for PSTN, and ISDN2 and ISDN30 services after September 2023.

It’s an understandable decision, given that PSTN and ISDN technologies rely on the same principle of copper wiring that Alexander Graham Bell patented right back in 1881. But with as many as five million lines currently active, businesses right across the UK will be affected.

What action you need to take depends upon your current infrastructure:

  • If your current ISDN contract is due for renewal soon, then now is the time to consider your options. Depending on your circumstances, you could either replace your entire existing system with a new VoIP (Voice over IP) system, or you might be able to switch to SIP (Session Initiation Protocol), enabling you to connect some, or all, of your existing phone system to the public network via IP data services.
  • If you don’t yet have a business telephony system installed, then you could consider a Cloud based telephony or collaboration solution, avoiding the setup costs associated with ISDN systems, and bypassing the need for physical infrastructure altogether.

However, this isn’t a binary decision, and nor should it be. As the last few months have shown, businesses of all sizes, in all sectors, have had to change the way they operate forever. Their priorities are now about:

Flexibility – paying only for the services you use; scaling up or down at short notice; moving or downsizing office estates.

Mobility – enabling more staff to work from home, or remotely; collaborating effectively with clients and colleagues, with remote file access; conducting increasing numbers of team and project meetings online.

Security – ensuring that mobile phones, tablets and devices are connected securely, regardless of their location.


That’s why O2 is working to develop the next generation of voice services – including services such as SIP and other advanced Unified Communication services. With mobility at the heart of everything we do, we are ideally placed to support businesses to grow and become more mobile now and in the future.

We are working with our existing customers to profile their legacy fixed estate to see what options would be most effective to help them to continue service following the ISDN switch-off. For many, switching to SIP Trunking is the ideal option:

  1. They can retain existing, trusted numbers, regardless of their business location.
  2. They can operate an ‘always on’ service, wherever their premises are located.
  3. They can benefit from call and data savings, as well as reduced maintenance costs of fixed systems.

We are also incorporating Unified Communications Platforms and Tools that deliver even greater benefits, such as remote working and enhanced collaboration – using a VoIP phone or their mobile to make and receive calls anywhere in the world, exactly as if they were in the office.

Using Unified Communications renders the distinction between fixed and mobile largely irrelevant, helping people to collaborate securely and flexibly with instant messaging and group conferencing on any device, from any location, and with just one number to use.


Why O2?

With O2’s mobile heritage, we are well placed to deliver flexible solutions that integrate fixed and mobile, keeping your people connected so they can work better together.

This convergence of fixed and mobile networks that led us to develop O2 Gateway, our single enterprise grade infrastructure that integrates fixed, mobile and Wi-Fi networks into a single platform.

As the UK’s first CAS(T)-certified mobile and WAN provider, O2 Gateway makes integrated connectivity both secure and robust, and is managed with a single end-to-end SLA and a dedicated point of contact to deal with.

With O2 Gateway, your IP based phone service is just one component of your unified, integrated communications system.

It’s your choice

In our experience, when businesses begin to explore the many benefits and advantages of VoIP and SIP Trunking systems, they choose to migrate sooner rather than later. From our conversations with businesses, the primary factor that causes them to delay migrating is the scale of investment in legacy infrastructure, and a need to continue to ‘sweat the assets’.

If it’s the right solution, then the good news is that switching the ISDN side of a customer’s estate to SIP is relatively straightforward. Existing numbers can be ported and retained, much existing infrastructure can be accommodated, and the new IP based service can be up and running within a few months.

However, a quick Google search might suggest that switching ISDN to SIP is your only choice. It isn’t. As a communications system specialist, we are here to help. Wherever you are starting from, we can support you to make the transition from ISDN, and establish a fully hosted communications system that is scalable, flexible, mobile and secure.

Regardless of size, our approach remains the same, and we follow the same, trusted three-step process:

1. Manage

We’ll bring all your PBX and line rental services under one contract, with one service level and one point of contact. Taking full ownership of your PBX services estate, freeing up your time to focus on your business.

2. Optimise

We know our services are competitively priced, but we can help you become even more cost-efficient by combining new and old technologies under one contract. And if your current PBX estate isn’t up to today’s standards, we’ll let you know how we can help.

3. Transform

We’ll keep you up-to-date on the latest industry changes so you can see how they’ll affect your organisation. If you’re ready to make changes, we’ll give you expert advice on the best options for you.


O2 Voice for Microsoft Teams

The increasing need for flexible and collaborative ways to work has led us to develop O2  Voice for Microsoft Teams, our forthcoming solution that provides telephony (PSTN) access into Microsoft Teams, replacing or reducing legacy platforms, while ensuring that users can continue to make ordinary calls to and from fixed and mobile devices. It will help businesses to reduce their overall telecoms spend by leveraging existing Office 365 licenses to replace traditional PBX costs. It’s ideal for any business looking to establish a connected and flexible approach to work.


Get in touch

If business communications form the critical component of your organisation then we’d love to talk with you about our secure and resilient service.

For more information on O2, our enterprise offerings, and our experience in SIP Trunking and unified Communication solutions, please call 01235 433507 or complete the business enquiry form.


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