[asterisk-users] Remote connection to an Asterisk server

[Gary]

I've been reading this forum for over the past 4 years and have gained a
wealth of knowledge. - Thanks to all!

I don't post very often but I've just ran into a problem/condition that I
simply can't figure out. - Hopefully some kind soul will help me.

I've got an Asterisk server in a lab environment on my home LAN. - The LAN
is "talking" to the Internet via a Linksys WRTG-54 router connected to my
cable-modem. - On the home LAN, I've also got a couple of Cisco phones
(7940's) and they work fine talking back and forth with each other via
Asterisk.

In fact, I've also got a Broadvoice account with a 7960 logged in all the
time and it works fine.  So I know SIP works through my router.

On the router, I've turned on "DMZ" to point to my Asterisk box's static IP
address.

My home (real world) IP address is static.

The Problem:  When I grab one of my Cisco 7940's and take it to my office,
it does not "see" or "register" with my home Asterisk server after I change
it's proxy to point to my home IP address.

Any Ideas? - Is this a router issue (sure seems like it)? - Much thanks in
advance.

Gary G.