Testing if phone number in service?

Hi All,

Sorry, this isn’t strictly a FreePBX question, but as there are lots of people in here with good knowledge of phone systems it seems an appropriate place to ask.

I’m looking for a method to test if a phone number is in service by interrogating the network. We are based in the UK and calling UK numbers and I’d like a way to weed out bad numbers from our databases.

I’m not looking for a system that relies on database lookups from the phone book, or good number ranges. I need to get a reliable result for individual numbers.

I’ve found a couple of companies that seem to be offering a service like this - http://www.data-8.co.uk/integr8/services/live_number_testing.aspx and http://number-testing.co.uk/?page_id=4

The descriptions of these services suggest that they are able to connect to the network and test if the number is in service transparently without causing the number to ring etc. I’m hoping we might be able to replicate this kind of functionality, possibly using Asterisk.

Can anyone suggest how these services might work? I’m thinking there may be something in the ISDN protocol that allow testing if a number is in service, or returns a status code before connecting the call.

I need a solution that’s legal, compliant with Ofcom guidelines and not going to annoy people so placing a brief call to see if it rings is not acceptable.