asterisk users - Jul 2007 - IP Trunk between Asterisk and another IP PBX

Dears;

If I need to do an SIP Trunk between Asterisk and
another IP PBX, then no need to do registeration to
that IP PBX (it the other IP PBX support this)?

In this case, do I need to make the host an static IP
address? Or what is the method to determine that no
registeration?