[Asterisk-Dev] Answer Supervision for incoming calls in Asterisk

[Kevin P. Fleming]

Adam Goryachev wrote:

> Is there some known work-around for this? Even if we could 'detect'
> this, and then answer the call before playing the welcome message?
> Somehow, I don't think that's possible though, which means either some
> people hear a lengthy silence, while others will hear things as normal.

I don't believe it's possible to know when this is happening, no. The 
thing is, the reasons it happens are varied: sometimes it's because the 
telco on the calling end disallows it, sometimes it's because the 
equipment on the calling end can't support it.

> PS, what if you wanted to use this feature for a 1800 number, to reduce
> your (the receivers) cost? Or for a normal number where most of your
> callers are long distance, and hence you want to reduce the callers cost
> while waiting for a real person to answer.... ie, doesn't need to be a
> premium rate number, there are plenty of other places it might be used.

Yes, it can be used in a variety of ways. Some big-company PBX systems 
use it so that when you call a DID for an employee and get their 
voicemail, the call is not 'answered' until their greeting has finished 
playing, which allows you to hang up without leaving a message and 
without being billed for the call.

> Thus, each of the 2xPSTN lines are one-way, but in different directions.
> Overall effect, is free phone call.... Sure, it is really messy, and
> maybe it wouldn't work in all circumstances, but it was just a
> thought :)

Early audio like this has a very short time window; I'd be surprised if 
very many telcos let you send early audio for more than 15-20 seconds 
before dropping the call if you don't answer it.