ISDN & PSTN Switch Off 2027: A Reseller's Migration Guide

The UK's ISDN and PSTN network is being switched off, and every business still relying on analogue or ISDN lines will need to migrate before it happens. Here's what's actually changing, when, and how resellers can turn it into an opportunity rather than a scramble.

What's Actually Being Switched Off?

PSTN (Public Switched Telephone Network) is the traditional analogue phone network that's underpinned UK phone lines for decades. ISDN (Integrated Services Digital Network) is the digital successor that many businesses still use for their phone systems, typically in the form of ISDN2 or ISDN30 lines. Both are being retired as Openreach moves the entire national network onto an all-IP infrastructure.

This also affects WLR (Wholesale Line Rental) — the underlying product that analogue lines are typically built on. If a customer has a WLR-based line, it's affected by the same withdrawal, even if they don't think of it as "ISDN."

What Replaces ISDN?

There isn't a single like-for-like replacement — the right option depends on what a business actually needs:

• SIP trunking — the closest direct replacement for ISDN. It connects an existing on-site phone system (PBX) to the phone network over an internet connection instead of a physical ISDN circuit, so businesses with a PBX they're happy with can often keep it and just change the connection method.
• Hosted PBX — a full move to a cloud-based phone system, removing the on-site PBX entirely. This suits businesses ready for a more complete upgrade, particularly if their current on-site hardware is also ageing.

Our SIP trunking guide and hosted PBX guide cover both options in more depth, and our hosted PBX vs SIP trunks comparison is worth reading if you're not sure which fits a given customer.

What This Means for Your Customers

Any customer still running ISDN, analogue lines, or an on-site phone system connected via WLR needs a migration plan before the network goes dark. Left too late, this isn't a gentle transition — it's a hard cutover, and a business with no working phone lines is not a conversation anyone wants to have after the fact.

The practical risk isn't just losing the customer's phone service. It's the customer discovering the switch-off from somewhere other than their current supplier, and moving their business to whoever gets there first with a proper migration plan.

Why This Is an Opportunity for Resellers

• Every affected customer needs to move eventually — this isn't optional, speculative demand. It's a guaranteed, time-bound reason to have a genuinely useful conversation with every ISDN customer on your book.
• It's a natural upsell moment — a forced migration is the ideal point to move a customer onto a better, more capable system rather than a like-for-like swap.
• Early movers win the relationship — customers who migrate well ahead of the deadline remember who made it easy. Those who wait until the last minute are far more price-sensitive and far more likely to shop around.

How Plustel Supports the Migration

Plustel's wholesale SIP trunks and Cloud X hosted PBX both give partners a straightforward migration path for ISDN customers, provisioned and managed through the same Zeus partner portal as the rest of our range. Because we run our own switch rather than reselling someone else's platform, migrations and any support issues that come up along the way get resolved directly, without being passed up a chain to a third party.

If you're planning ISDN migrations across your customer base, our team can talk through timing, which customers are the best fit for SIP trunks versus a full hosted PBX move, and how to structure the conversation so it lands as an upgrade rather than a disruption.