Nortel i2001 running over Asterisk

I really do not have any idea why when I connect two (2) nortel phones under Asterisk using unistim.conf, One works and the second does not.

I was running a sniffer in order to get some differences and I placed a call from a computer with a softphone (SIP) and WireShark. I got the packages. I saw that with the phone who works, the Server and softphone send and receive RTP packages (both directions) and the other case (not working phone) just softphone send RTP packages but Server never answer