PSTN Switch Off
Moving legacy PSTN-connected assets to secure IP.
BT has announced that PSTN and ISDN services will stop working from 31 January 2027 if they have not been moved to an IP-based alternative. This does not only affect phone systems. It also affects meters, modems, alarms, lift lines, telemetry, payment systems and other equipment that quietly depends on analogue phone lines.
Why it matters
The biggest risk is the line nobody knows about.
For many organisations, the PSTN switch off is not just a telecoms project. It is an operational risk. Legacy lines are often hidden in plant rooms, meter cupboards, lift shafts, alarm panels and remote sites. They may not appear in normal IT inventories, but they still support important business processes.
GridSecure specialises in identifying these services and moving them onto secure, supportable IP-based connectivity without simply exposing operational devices to the public internet.
Services commonly affected
PDPL
Pre-Digital Phone Line is a bridge, not the destination.
BT’s Pre-Digital Phone Line service can help some legacy devices move away from the PSTN where an immediate full IP migration is not yet possible. However, PDPL is temporary. It does not remove the need to upgrade the physical site, the device connection or the long-term communications design.
Even if your wider telecoms estate has moved to SIP trunks, a legacy field device may still be relying on an analogue service at the edge. When that asset is eventually replaced with an IP capable device, the PDPL service becomes obsolete.
What PDPL means in practice
- ✓Useful where a legacy asset cannot move immediately
- ✓Still requires testing against the actual device
- ✓Does not remove the need for IP migration planning
- ✓Should be treated as a temporary service only
Identify every PSTN dependency
Many PSTN lines are not obvious phone lines. They may sit behind meters, modems, alarm panels, lift lines or remote operational equipment.
Decide the right access method
Sites may need FTTP, SoGEA, satellite, PDPL as a temporary bridge, or a more tailored managed WAN design.
Move the asset to IP
GridSecure can help replace dial-up style access with secure IP connectivity, private routing and controlled access.
Monitor and support the estate
The GridNet platform can help monitor site uptime, tunnel status, device reachability and support tickets.
Case study
Large estates need mapping before migration.
A published rail infrastructure case study described an estate with more than 8,000 PSTN lines supporting remote safety-critical equipment such as signals, crossings, ticket machines, alarms and emergency phones. The key lesson is clear: PSTN migration is not only about replacing phone lines. It is about understanding every connected asset, who owns it, what it does, and how it should be reached after the move to IP.
GridSecure can help
Need to move PSTN-connected devices to IP?
GridSecure Networks can help identify affected sites, select the correct WAN service, configure secure routing, provide managed access and support the ongoing service through GridNet monitoring, helpdesk and ticketing.