What is an HLR lookup and what can you do with it?

An HLR lookup asks the mobile network whether a number exists and is active — without sending a message.

What you get back

Whether the number exists, which network it belongs to, which country it belongs in, and whether it was ever ported to another operator. That last point is useful because the country code then no longer matches the actual operator.

What you use it for

Cleaning lists before a campaign. Validating numbers at the moment somebody enters them, so a typo is visible straight away. And route selection, because with the right network the message takes the direct route instead of a detour.

What it does not do

It says nothing about who owns the number, and nothing about whether the device is switched on at that moment. An active number with a switched-off device simply returns "exists".

What it costs

A fraction of an SMS. On a list with many dead numbers it pays for itself on the first campaign.