I had a similar problem on a laptop using Fedora 3. After installing the conexant chipset driver, I could then see the modem in the device list. Go to
http://www.linuxant.com/drivers/ They have drivers for conexant chipsets which are very easy to install, with excellent instructions. They offer a free driver with a maximum connection speed of 14.4kps or for $14.95 you can get the full version. Once the driver is loaded you should then be able to see your modem. If you still encounter problems using fedora 4, try using Fedora 3.
Good Luck