Openreach’s programme to decommission the UK’s public switched telephone network (PSTN) — including all ISDN2 and ISDN30 lines — is the most significant forced migration event in UK telecoms in a generation. The full switch-off is scheduled for 2027, and in most exchange areas Openreach has already stopped accepting new ISDN orders. For telecoms resellers and IT providers with business clients on ISDN, the question is no longer whether to act but how early to start.
What the PSTN Switch-Off Actually Means
The PSTN is the infrastructure that underpins traditional telephone lines, including ISDN business channels, analogue PSTN single lines, and ADSL or FTTC broadband delivered over the copper network. Openreach is retiring this infrastructure and migrating all services to IP-based equivalents. When the switch-off is complete in a given exchange area, ISDN lines will cease to function. Businesses that have not migrated will lose their phone service.
This affects not just phone systems but any device or service that uses the PSTN: alarm lines, EPOS terminals, door entry systems, lift emergency lines, and fax machines. A full audit of a client’s PSTN dependencies is the starting point for any migration project.
Which Clients Are Affected?
The switch-off affects businesses running:
- ISDN2 or ISDN30 lines connected to a traditional PBX — common across SMEs, schools, healthcare practices, solicitors, and hospitality businesses that have not yet migrated to VoIP.
- Analogue PSTN single lines used for fax, payment terminals, alarm monitoring, or lift emergency calls.
- ADSL or FTTC broadband delivered over the legacy copper PSTN — these need to move to SoGEA or FTTP.
The scale of the affected base is substantial. Most IT resellers and telecoms providers with any legacy SME clients will find a significant proportion still running ISDN or PSTN-dependent services.
The Replacement Stack
A complete ISDN migration typically involves three components:
- Broadband: SoGEA (the PSTN-free equivalent of FTTC) or FTTP (full fibre) provides the IP connectivity the new system requires. X2 offers wholesale broadband access to all major UK network operators.
- VoIP platform: A hosted or on-premise IP PBX. X2 specialises in Yeastar P-Series — available as a cloud PBX on a 30-day rolling contract or as a hardware appliance for clients who prefer on-premise infrastructure.
- SIP trunking: Replacing ISDN channels with SIP trunks provisioned through Telnyx or Voiceflex. Number porting preserves the client’s existing phone numbers with no visible change to callers.
X2 manages the full technical migration: system provisioning, trunk configuration, number porting, and handset deployment. As the reseller, your role is to manage the client relationship and the migration timeline.
The Commercial Opportunity
Every client still running ISDN is a mandatory upgrade conversation waiting to happen. Resellers who initiate that conversation proactively — before clients receive letters from Openreach or before deadline pressure forces a reactive migration — are better positioned to retain those clients on a managed VoIP contract and to manage the transition on a timeline that works for both parties.
The opportunity extends beyond the phone system. A client migrating from ISDN typically also needs a broadband upgrade, and may be open to conversations about mobile softphones, Teams integration, call recording, and AI voice analytics — all of which represent additional recurring revenue. To discuss PSTN migration planning for your client base, speak to the X2 team.