[Asterisk-Users] ISDN BRI and UK Premium Rate Numbers

[Faris Raouf]

Can anyone help point me in the right direction please?

I'm based in the UK and I want to start using a Premium Rate number with 
Asterisk - I think the equivalent in the US would be a "900 number". 
Effectively the caller pays much more to call such a number than a 
normal national or local call.

The problem with these is that I don't want Asterisk to actually signal 
to the telephone network that the call has been answered until someone 
really does answer it, otherwise the caller will be paying a premium 
rate just to listen to an Asterisk-generated ring tone until someone 
answers the call.

My setup would be chan_capi-cm and an ISDN BRI line with several MSNs 
(not DDIs -- this line does not support point-to-point only point to 
multipoint but we do have another line that does do point to point and 
has DDIs, and if necessary we can use it), and of course Asterisk and 
various SIP phones.

I have very little idea where to start, as everything I normally do with 
Asterisk involves the call being answered immediately then put in a 
queue, which is no good in this case.

What I really want is for the call to come in then:
1) One or more SIP phones will ring (unless they are on a call) but for 
Asterisk not to signal an "answer" just yet
2) Only when someone is free and answers the call does asterisk "answer" 
and put them through.

Ideally I'd also like the caller and the person answering the call to 
hear a recorded message saying that calls to this number cost X per 
minute ... blah blah...., this message being triggered only when someone 
answers the call. This will warn the caller *and* the person answering 
that this is a premium-rate call. The person answering the call will 
know to speak after this message has been played. But that's just an 
ideal situation. Right now I'm more concerned about how to stop Asterisk 
answering until someone is available to take the call.

Can anyone help please? I don't really know where to start. The Wiki 
seems to be pointing me towards using DID/DDIs, but that's about as far 
as I've got.

NOTE: We don't need the actual Premium Rate numbers themselves. We have 
those already (we used them with an old telephone system until 
recently). My problem is just to get Asterisk to work with them in the 
way I've outlined.

Faris.