Let me try answer. Tehcnicly we are speaking about SIP Early Media feture and you can define that in campaing settings (Dialing Settings tab) Early Media option. Then at backend we have a piece of code that should detect the Early Media messages. The codes backend is expecting:
0 AMD timeout expires, no signal was detected (configured by the parameter AMDTimeout).
1 Answering machine was detected.
2 Call forward on no answer was detected.
3 Call forward on busy was detected.
4 Fax was detected.
5 Modem was detected.
6 Not supported in the current version.
7 Silence was detected.
8 SIT was detected.
Before you get exited I have to say that we haven't seen this in action yet and no prove that it works as should. Maybe we should try it out together and see how it works. I will have a discussion at our side and see if that could be arranged.