Routing issue..updated question..connectivity

Ok, Guess I need to rephrase this.
I am trying to set up the system so my brother can setup a sip phone in Florida and connect it to my server in Tennessee. Would he need to setup the gateway as my dsl modem and let the router forward it to the ip on the server or should it be setup to the router ip and let it get past on to the box? Not sure which direction to go. Any help is much appreciated.
Thanks,
Bill

I am in Tennesse and my brother is in Florida. I want him to beable to access the freebx gui by entering a domain name in the web browser. I am not sure how to make that happen. I know I have to point my domain name towards my at&t modem. say that is ip 0.0.0.1. I have the system setup on a router and the box address for asterisk is 196.148.2.4. Can anyone point me in the right direction…I am new to asterisk as you can tell. Seems to be a great system so far.
Thanks,
Bill