HT 488 ATA with asterisk

I have Bought Grandstream GXP 2000 (IP Phone) and HT 488 (ATA with 1FXS and 1 FXO)
I have compiled asterisk 1.4 on Fedora Core 7, Configured the GXP 2000 (it works fine)
But i’m getting a hard time with HT 488

This is how my setup looks

===================MODEM===ROUTER===All Machines and Devices connect Here

I have connected a cable from router to wan port of HT488 PSTN line and a telephone in specific ports
The analog telephone is able to register with Asterisk sip a/c. But i’m not sure how to use and route asterisk calls through PSTN FXO.

Please Help

Does anyone have a solution