I am Trying very unsuccessfully to setup a SIP Gateway or SIP router.
In brief I need FreePBX to accept any incoming call and then route it out a SIP Trunk.
Any help is greatly appreciated.
I think you are looking for the same thing I am. You want some sort of SIP front end and handles your connection to the PSTN on the WAN side, and on the LAN side, provides trunks for multiple PBX’s, that routes the outgoing traffic from either PBX out through the single trunk. I’ve been working on finding something to do that for a while, without spending $10,000.00. SIP Express Router - http://www.iptel.org/ser, OpenSER / Kamailio - http://www.kamailio.org/w/ and even SipXecs - http://wiki.sipfoundry.org/display/sipXecs/Home They are all “Supposed” to front end for Asterisk or by default FreePBX. You may want to start looking there and see what you find, as for anyone else in this forum, I would appreciate any input on this subject also. 
Well OpenSIPS works great and does exactly what you want. So does Freeswitch. I just find Freeswitch more flexible.