If the modem is a Conexant HSF modem, download
this driver and install it like this:
1. extract the package with "tar -xzf hsflinmodem-{version}.tar.gz"
2. change to the package directory with "cd hsflinmodem-{version}"
3. run "make install" from the top of the package directory.
(Debian users might need to change the KERNELSRC definition in
modules/common.mak first)
4. run "hsfconfig" to complete the installation and configure your modem.
Just make sure you do this as root. This is the older non-speed-locked version.
Baldrick