asterisk users - Sep 2005 - How to tell reason for hangup or busy in SIP or IAX

Hi,

using Zap, I have several messages to pass when
terminating a successful or unsuccessfull call,
indicating the reason e.g., why a call failed.

Using SIP or IAX2, I know only

Hangup
Busy
Congestion

without passing any more detailed information.

Am I right, that I can't tell the caller in SIP or IAX2,
whether the call was rejected or whether the called
number does not exist.

I have to assign those "hangupcauses" to one of

Hangup (which I use for normal termination after
    successfull call and for "No answer" after timeout.

Busy (which I use, if the called phone is busy)

Congestion (which I use, if our gateway or one of the used carriers
    are busy)


Thanks for any hints, if there further means!
Roger.