ISDN Switch Off: What UK Businesses Need to Know Before 2025

isdn switch off

The UK’s ISDN switch off is approaching fast. By December 2025, BT will shut down the ISDN and PSTN networks that have underpinned the UK’s business phone infrastructure for decades. For small and medium-sized enterprises (SMEs), this represents a critical shift—one that demands preparation and smart decision-making.

At Digi Toolbox, we help Hampshire-based businesses navigate these digital transitions with clarity and confidence. In this guide, we’ll explain what the ISDN switch off means, why it’s happening, and—most importantly—what steps your business should take to stay connected and competitive.

Why Is the ISDN Switch Off Happening?

ISDN (Integrated Services Digital Network) was first introduced in the UK in the 1980s. While it served its purpose for many years, it has become outdated due to the rise of more efficient and flexible technologies like VoIP.

Key Drivers Behind the ISDN Switch Off:

  • Ageing Infrastructure: Maintaining ISDN lines is costly and inefficient.
  • Limited Functionality: ISDN doesn’t support modern communication features like video calling and cloud integration.
  • Digital Transformation: Businesses are shifting towards cloud-based solutions and unified communications.
  • Environmental Considerations: Phasing out ISDN contributes to greener, more sustainable technology.

The switch off will affect all voice services over the PSTN, including traditional phone lines, ISDN2, and ISDN30. That’s millions of businesses that need to act now.

Who Will Be Affected by the ISDN Switch Off?

Any business still relying on:

  • ISDN phone lines
  • Analogue landlines
  • Legacy phone systems
  • Alarm or fax systems using the PSTN

If you haven’t transitioned to IP-based solutions, your business communications will be disrupted in 2025.

Digi Toolbox offers a full range of telephony solutions, including VoIP, hosted phone systems, and SIP trunking, designed to help you make the switch smoothly and affordably.

What Should Your Business Do Now?

1. Audit Your Existing System

  • Identify what services are connected to the PSTN or ISDN lines.
  • Include phones, broadband, alarms, payment terminals, and lift phones.

2. Upgrade to IP-Based Solutions

VoIP (Voice over Internet Protocol) is the go-to replacement for ISDN. It allows voice communications over your broadband connection.

Benefits of VoIP:

  • Lower call costs
  • Greater flexibility and mobility
  • Advanced features like voicemail-to-email and call analytics
  • Scalability without hardware constraints

At Digi Toolbox, we provide bespoke VoIP packages for businesses of all sizes.

3. Check Internet Capability

VoIP and other IP-based systems rely on a robust internet connection.

We offer fibre broadband and leased line services to ensure uninterrupted, high-quality communications.

4. Future-Proof Your Communications

Opt for solutions that can evolve with your business. Our hosted phone systems are fully scalable and come with built-in disaster recovery, ensuring your business remains resilient and agile.

If you would like to find out more, please get in touch with us to discuss your requirements or book a meeting with a specialist at a time that works for you.
Phone: 01489 297070
Email: [email protected]
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FAQs About the ISDN Switch Off

When is the ISDN switch off happening?

BT plans to retire the PSTN and ISDN networks by December 2025. A national stop-sell of new ISDN services was implemented in September 2023.

Will I need to change my phone number?

No. Number porting allows you to retain your existing number when switching to VoIP or hosted solutions.

What happens if I don’t switch before the deadline?

Your phone services will stop working. This includes calls, alarms, card machines, and broadband if they run over ISDN or PSTN lines.

Is VoIP more expensive than ISDN?

No—VoIP is typically more cost-effective. You’ll benefit from lower call charges, especially for international calls, and fewer infrastructure costs.

Can I use VoIP with my current internet plan?

Possibly. However, for best results, a fibre or leased line is recommended to support voice quality and reliability.

Start Your Project Today

At Digi Toolbox, we’re more than just a digital agency—we’re a partner dedicated to understanding your business and helping you achieve your goals. That’s why we take a consultative approach to discovery, ensuring that every solution we provide is tailored to your unique requirements.

We offer a free discovery consultation, which can be conducted in the way that suits you best: face-to-face, at our office, via Microsoft Teams, or over the phone. This flexibility ensures that no matter how you choose to connect with our digital agency, the process is convenient and designed around your needs.

To deepen our understanding of your business, we also provide free audits covering digital marketing, IT, and telephony. These audits give us valuable insights into your existing systems, allowing our team to identify opportunities for improvement and create bespoke strategies. By taking the time to analyse your business, we ensure that every recommendation we make is perfectly aligned with your objectives.

At Digi Toolbox, we take pride in being a digital agency that puts your business first. With our consultative approach, we’ll deliver personalised solutions to drive your success. Let’s start the conversation. Contact us today to discuss our digital agency solutions today!