APN....Routing or port forwarding?

[reaper732]

I need help.

let me first provide my current network infomation
I have a cisco 1811 adsl router with a static ip address.the routers ip is 10.1.0.1/24
the network ip range is 10.0.0.1/24(internal)
between the router and the network i have a linux box witch serves the same purpose as untangle.with the 1 nic ip 10.1.0.2 and the secound nic`s ip 10.0.0.2(so the linux box routes packets from the 10.1.0.0/24 network to the 10.0.0.0/24 network to give the intenal network internet access)
the network gets internet and everything is working fine.
the trick is i am trying to use a mobile apn. with is a 3g modem routed to the adsl also hosted by the mobile network company.
the modem recives an ip of 172.16.1.1 netmask 255.255.255.255

when im connected to the 3g(apn) i can ping 10.1.0.1 and 10.1.0.2 but i cant ping any of the 10.0.0.0 network .
the plan is to try untangle because it`s not linux and remove the linux box
if anyone can help me how i should configure untangle i would appreciated it