Critical Dates and Preparation Steps for the 2026 ISDN/PSTN Switch-off in Sussex
The telecommunications landscape across the UK is undergoing its most significant transformation in decades. For Sussex businesses, understanding the ISDN/PSTN switch-off timeline is no longer optional—it’s essential for ensuring business continuity. With the December 2026 deadline approaching, now is the time to prepare your organisation for this fundamental change in business communications.
At Structured Communications, we’re guiding Sussex businesses through this transition with tailored VoIP solutions designed to minimise disruption and maximise opportunities. This comprehensive guide outlines the critical ISDN/PSTN switch-off timeline and practical steps your business should take to prepare.
What Exactly Is Being Switched Off in the ISDN/PSTN Switch-off?
Before diving into the ISDN/PSTN switch-off timeline, it’s important to understand what technologies are being decommissioned:
PSTN (Public Switched Telephone Network)
The traditional copper telephone network that has served Sussex businesses for over a century. Single lines (Home and business), services such as fax, alarm, lifts, PDQ machines.
ISDN (Integrated Services Digital Network)
Digital telephone lines that have been the backbone of business communications since the 1980s, including:
- ISDN2: Providing combinations of two digital channels (2, 4, 6, 8), typically used by smaller businesses
- ISDN30: Offering up to 30 channels, commonly used by larger organisations with PBX systems
According to Ofcom’s latest update, these technologies are being replaced by IP-based solutions that offer greater flexibility, features, and cost-effectiveness for businesses throughout Sussex and beyond.
The ISDN/PSTN Switch-off Timeline for Sussex Businesses
The ISDN/PSTN switch-off is not a single event but a phased process with several key milestones:
Phase 1: Stop Sell (Already in Progress)
- What it means: Openreach has already implemented a “stop sell” policy in many exchanges, including all in Sussex.
- Impact on Sussex businesses: You can no longer order new ISDN or PSTN lines in affected areas.
- Sussex exchanges affected: Horsham, Crawley, and parts of Worthing are already under stop sell conditions.
Phase 2: Managed Migration (2025-2026)
- What it means: Businesses are being actively encouraged to migrate from ISDN/PSTN to IP-based alternatives like SFlow VoIP.
- Impact on Sussex businesses: This is the optimal window to plan and implement your migration with minimal pressure.
- Current status: We are in this phase now—the ideal time for Sussex businesses to act before the ISDN/PSTN switch-off deadline.
Phase 3: Final ISDN/PSTN Switch-off (December 2026)
- What it means: All remaining ISDN and PSTN services will be decommissioned permanently.
- Impact on Sussex businesses: Any organisation still using these technologies will lose service completely.
- Countdown: The clock is ticking toward the final ISDN/PSTN switch-off date.
Sussex-Specific ISDN/PSTN Switch-off Schedule
The ISDN/PSTN switch-off is happening at different times across different exchanges. For Sussex businesses, here’s the current schedule:
Horsham Exchange
- Stop Sell: Already implemented
- Migration Focus: Currently in progress
- Final ISDN/PSTN Switch-off: December 2026
Crawley Exchange
- Stop Sell: Already implemented
- Migration Focus: Currently in progress
- Final ISDN/PSTN Switch-off: December 2026
Worthing Exchange
- Stop Sell: Partial implementation
- Migration Focus: Currently in progress
- Final ISDN/PSTN Switch-off: December 2026
Chichester Exchange
- Stop Sell: Scheduled for Q3 2026
- Migration Focus: Currently in progress
- Final ISDN/PSTN Switch-off: December 2026
Rural Sussex Exchanges
- Stop Sell: Various implementation dates throughout 2026
- Final ISDN/PSTN Switch-off: December 2026
What Sussex Businesses Need to Do Now Before the ISDN/PSTN Switch-off
With the ISDN/PSTN switch-off timeline advancing, here are the essential steps your Sussex business should take:
- Audit Your Current Telecommunications Infrastructure
Identify all systems reliant on ISDN/PSTN:
- Phone systems
- Fax machines
- PDQ/card payment terminals
- Door entry systems
- Alarm systems
- Lift emergency phones
Why this matters: Many Sussex businesses are surprised to discover how many critical systems rely on traditional phone lines. A comprehensive audit is essential for planning your migration before the ISDN/PSTN switch-off.
- Assess Your Connectivity Requirements
Before migrating to VoIP, ensure your internet connectivity can support it:
- Standard Broadband: May support basic VoIP needs for very small businesses
- Fibre Broadband: Suitable for small to medium businesses with moderate call volumes
- Leased Lines: Recommended for businesses where call quality is critical
Why this matters: VoIP call quality is directly related to your internet connection quality. Our connectivity solutions are designed to ensure optimal VoIP performance for Sussex businesses.
- Develop a Migration Timeline
With the final ISDN/PSTN switch-off date approaching, create a phased migration plan:
- Q3 2025: Complete your telecommunications audit and connectivity assessment
- Q4 2025: Select your VoIP provider and solution
- Q1 2026: Begin implementation and testing
- Before December 2026: Complete full migration with overlap period for troubleshooting
Why this matters: A phased approach minimises disruption and allows for testing and adjustment before the final ISDN/PSTN switch-off deadline.
- Choose the Right VoIP Solution
Select a VoIP system that meets your specific business requirements:
- SFlow VoIP Platform: Our comprehensive solution offering features like mobile integration, call recording, and CRM connectivity
- SIP Trunking: For businesses wishing to maintain existing PBX hardware
- Microsoft Teams Integration: For organisations already using Microsoft 365
Why this matters: The right solution depends on your specific business needs, size, and existing technology investments as you prepare for the ISDN switch-off.
Common Questions About the ISDN/PSTN Switch-off Timeline
Will my phone numbers change during the migration?
No, with proper planning your existing business numbers can be ported to your new VoIP solution.
How long does migration typically take?
For most West Sussex businesses, the complete migration process takes 4-8 weeks, depending on complexity and number of services.
What happens if I don’t migrate before the ISDN/PSTN switch-off date?
Your telecommunications services will cease to function, potentially causing significant business disruption and loss of numbers.
Will VoIP provide the same call quality as ISDN/PSTN?
With appropriate connectivity, VoIP call quality typically exceeds traditional ISDN & PSTN quality while offering additional features and flexibility.
How disruptive is the migration process?
With proper planning and a phased approach, disruption can be minimised or eliminated entirely.
How Structured Communications Can Help Sussex Businesses with the ISDN-PSTN Switch-off
As a Sussex-based telecommunications provider with over a decade of experience, we offer:
- Free ISDN-PSTN Switch-off Consultation: Comprehensive assessment of your current systems and migration requirements
- Tailored Migration Planning: Customised timeline and approach based on your specific business needs
- End-to-End Implementation: From initial audit through to complete migration and testing
- Ongoing Support: Local, responsive support from our Horsham headquarters
- Future-Proofed Solutions: Continuous updates and enhancements to our SFlow VoIP platform
Next Steps for Sussex Businesses Before the Switch-off
With the ISDN-PSTN switch-off timeline advancing, we recommend these immediate actions:
- Contact our West Sussex team for a free ISDN-PSTN switch-off readiness assessment
- Begin your telecommunications audit to identify all affected systems
- Review your current connectivity to determine if upgrades are needed
- Explore our VoIP solutions to identify the best fit for your business
According to BT Openreach’s official timeline, businesses should start planning their migration well ahead of the December 2026 deadline to ensure a smooth transition.
Call us today on 0203 301 4000 or email hello@structuredcommunications.co.uk to start your ISDN-PSTN switch-off preparation.
Structured Communications is the leading telecommunications provider for West Sussex businesses, offering VoIP, SIP, broadband, leased lines, and mobile solutions tailored to your specific needs. Based in Horsham at Unit 8 Foundry Court, Foundry Lane, West Sussex, RH13 5PY, we provide local expertise with enterprise-grade solutions. Rated 4.65/5 on Reviews.io based on customer feedback.
