Preparing for the UK ISDN/PSTN switch-off

Around the world, countries are phasing out their POTS/PSTN. Here's what to do if you're impacted.

If you’re a telecom professional or IT leader, you’ve probably heard about the looming Integrated Services Digital Network (ISDN), or Public Switched Telephone Network (PSTN), switch-off spanning Europe.

Countries like Estonia and The Netherlands have been switching off their ISDN for years–and now, it’s happening across more countries. Germany, Japan, and Sweden are following suit, and in 2025, the UK will completely retire its ISDN circuits via British Telecom (BT).

With an estimated impact of three million organizations across the UK alone, the PSTN switch-off can cause significant disruption. But with the right tools, partners, and knowledge, you can take your communications from copper wires to the cloud–all without breaking a sweat (or the bank). 

What is the ISDN/PSTN switch-off?

The ISDN switch-off has been around for a while, with different countries moving at their own pace. In 2015, BT announced that they’d be turning off ISDN and PSTN lines and switching to digital lines, or internet protocol (IP) lines. Businesses will be unable to procure analog telephony or purchase and renew contracts on ISDN circuits in countries at varying deadlines.  

This is forcing enterprises to modernize and relocate business operations in the cloud—including unified communications & collaboration, contact centers, third-party tools, and emergency calling. Businesses need to adopt Voice over Internet Protocol (VoIP) to communicate, likely in the form of SIP.

Copper wires vs. the cloud

There’s no event or reason that’s causing ISDN to become defunct, although age is a key factor. As technology becomes more important to daily life, the traditional copper network used to make and receive phone calls can’t keep up with cloud-based alternatives. 

By transitioning to digital communications, we’re making room for more efficient, effective solutions. The ISDN requires regular maintenance and upgrades and is vulnerable to disruption. At the same time, IP-based phone systems have developed and grown in popularity due to their scalable and cost-effective nature.  

And although migrating can be challenging, the shift is necessary. With VoIP communications, organizations can: 

  • Eliminate location-based requirements and physical phone lines, which is ideal for remote or hybrid employees
  • Quickly establish a presence in places where you do business, instead of installing on-prem equipment and connections
  • Reduce investments in on-prem equipment like PBXs & SBCs, so you can deploy comms faster
  • Integrate cloud-based tools into call flows quickly and deliver a smooth user experience

How to prepare for BT’s ISDN switch-off

Start migrating to IP-based communications now. The closer the deadline gets, the more everyone will run to the exit simultaneously. Migrating to the cloud is a complex exercise in change management, but the technology and solutions to achieve this exist. 

The most common forms of IP technology are VoIP and SIP. And with the right provider, your move can be an opportunity to build a best-of-breed communications stack, your way. 


VoIP allows users to make calls for a very low cost. The user uses voice to communicate over a broadband connection, and a reliable internet connection is vital for VoIP to work. 

1. Basic VoIP service plans include caller ID, call forwarding, and call waiting.

2. VoIP systems don’t require on-site installation and tend to be easy to transport.

3. Investment costs are typically low.

4. Most providers don’t require long-term contracts for service.
1. Lack of support for multimedia communications.

2. Can’t be integrated with some applications.

3. Requires bandwidth for call quality of service (QoS) and service availability.

SIP Trunking

SIP is a set of rules used in multimedia communications to initiate and terminate data transfer between different users. Consider the following pros and cons of combining the two:

1. Continuity Scales up and down as necessary.

2. Integrates with compatible Public Branch Exchanges (PBX).

3. Added flexibility to send MMS and video.

4. Cost savings by allowing for additional lines or features if necessary.

5. Improve integration with PRI lines.

6. Better integrate with cloud-based applications like UCaaS and CCaaS.
1. Can have issues with security and quality.

2. Not all SIP providers offer the same quality of service or features.

Your PSTN switch-off checklist

You’ve picked your communications protocol. Now, you need to determine how, where, and when you’re migrating. After you’ve mapped out your strategic goals and looped in your key stakeholders, use this checklist to migrate your communications without a hitch!


  • Scope the compliance challenges and requirements across your target countries
  • Prepare your tech stack to include both channel control and flexibility to integrate with new infrastructure
  • Ensure your network providers can provide you with consistent service across multiple geographies


  • Evaluate and create a shortlist of network providers that offer maximum cost efficiency for multi-regional operations
  • Double-check your carrier’s network reliability, uptime, and consistency of service
  • Look for 24/7/365 network operations and technical support
  • Pick your communications partner(s) based on how they will support you in moments of change, crises, and urgent needs
  • Understand how your network provider makes life easy for you in your day-to-day operations
  • Consolidate providers as much as possible for cost and operational efficiencies, without trading off redundancy and reliability


  • Think long-term cost-efficiencies while setting up your infrastructure in the target market(s)
  • Do you want to build or buy network services as you scale globally? Assess the pros and cons of each approach in terms of your growth strategy
  • Shift focus to growth and innovation by streamlining operations
  • Set up to identify and drive necessary roadmap innovations and coverage required to maintain growth velocity in the longer term
  • Stay conversant in telecom industry trends and position your network provider(s) to help leverage new developments to accelerate your own growth
  • Set up a process (or find a partner) to monitor regulatory changes and their implications to your current and future markets
  • Get insights from your network partner(s) into your own traffic to help you improve your customers’ experience

Prepare for the ISDN switch-off

Moving from on-premise to the cloud is no easy feat–but it’s been done before. For more resources to help you navigate this transition, explore our library or talk to an expert.