What Happens If You Don't Switch From PSTN or ISDN in Time?

What happens at the point of withdrawal

When a line is withdrawn, the service on it stops. Calls to your number will not connect, and outbound calls from that line will not place. There is no grace period on the line itself.

Anything else using the line goes at the same moment: alarm diallers, lift emergency lines, dial-up card terminals, door entry. Those failures are often noticed before the phones are.

Numbers that weren't ported can't be recovered

Porting is a transfer between providers that has to happen while the line still exists. Once a line has been ceased, the number goes with it, and there is no route to claim it back afterwards.

For most businesses that is the real exposure. Signage, vehicles, printed material, directory listings and years of customer records all point at one number. Replacing it costs far more than the migration ever would.

Lead times get longer as the deadline approaches

Migration isn't a single task. It's an audit, a number port with a fixed notice period, possibly new hardware, and often an installer visit for connected equipment such as alarms or card terminals.

• Porting runs to a scheduled timetable and can't be rushed by the losing provider
• Alarm and telecare installers have finite visit capacity across the same window
• Hardware lead times stretch when demand concentrates
• Your own team needs time to test and get used to the new setup

Every business left on an old line is queueing for the same finite capacity. Waiting doesn't reduce the work — it removes your ability to choose when it happens.

You may already be feeling stop-sell

The national stop-sell has been in force since September 2023, so no new analogue or ISDN lines can be ordered. If you've recently tried to add a line for a new office, a new till point or a temporary site and been told it isn't possible, that's why.

It also means the old network can't flex around a problem any more. Once a circuit is gone, the only forward option is a replacement service.

Starting a migration plan

You don't have to move today, but you should know what you'd be moving. Start with a list of every line you pay for, what's plugged into each one, and which numbers matter. That single document turns the whole thing from a worry into a task.

If you're on BT lines, our switching from BT page walks through how the move works and what changes on your bill. Send us the list and we'll tell you what's involved and roughly how long it takes.