When dialing from an FXS port you are not an "authenticated user" so
those variables from user directory don't get populated. You have two
choices as I see it:
#1 - Manually set the ${default_gateway} variable by inserting this
line before the bridge:
<action application="set" data="default_gateway=
gw4.telasip.com"/>
#2 - Use the set_user app (
http://wiki.freeswitch.org/wiki/Misc._Dialplan_Tools_set_user)
to make the call act like it was from an auth'd user:
<action application="set_user" data="1000@${domain}"/>
Give it a whirl and let me know how it goes.
-MC