Ok forgive me but, a silly question...
You didn't take the modem out? it's the rectangular card held in place with 4 screws? I helped a guy awhile back who took it out in order to have room to install a hard drive and didn't realize it was the modem; other than that there is no other modem unless you have a HPNA mini-pci then there is a soft 56k modem you can use; it requires the Gateway drivers. (the orginal GCT with HPNA didn't utilize the modem on the HPNA as the wasn't a driver under the Midora OS).
I do know that Windows XP detected a soft modem in one of mine once (not the regualer one or HPNA), but I never could find drivers for it and it was the only OS that detected a modem from the Ali chipset.