asterisk users - Jun 2005 - communication between IAX softphones

I tried with several iax softphones:
iaxcomm
idefix
iaxphone

and i have a problems that i do not have with SIP clients.

A calls B, B phone starts ringing, asterisk says that call has been 
accepted, that is ringing but it is not yet answered. If B "picks up",
asterisk says that call has been answered but, *before* User B pick up, 
he is already able to hear User A and viceversa.

ciao