asterisk users - Nov 2014 - Code send by asterisk when a peer hangs up

Hi

I have noticed that the code send by asterisk to some other party when a peer,
represented by a soft phone, hangs up is 486 (Busy here). The problem I see is
that when the user does not answer at all the same code is send by asterisk to
the other party. So there is no clear distinction when the user rejects the call
(by hanging up) or he is not available. Is there a way to configure asterisk to
tell the difference between a hangup and an user busy situation ?

thanks
Bogdan