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 While it served its purpose for many years, it has become outdated due to the rise of more efficient and flexible technologies like VoIP.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: hello@digitoolbox.com
Book a Meeting with a Specialist
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.
