Letting SIP client connect directly

I have an * server and two sip extensions registered on it, and they are in three different places.
SIP packets of course follow this path:
Then I want to connect my SIP client directly.
I worked hard tryng to do that, by changing all the parameters in the sip.conf (canreinvite, nat, dtmfmode, qualify),
but I’m not still able to do what I want.
I’ll post my conf files if someone wants help me.
Thanks in advance,

I partially solved my problem.
It was depending from the t (or T) option in some applications.
I’m going to write more on this, in particular how to configure SIP for direct connetions.
I hope it will be helpfull, and I hope someone helps me to test it.