Go
here and do a little reading, follow the link called scanModem tool, download and run it and it will tell you what modem you have, if it is supported in Linux, and where to get source for compiling drivers/modules, and much more useful information. Most of the important information you'll need will be written to a file called modemData.txt or similar in a folder called modem in the directory you are in when you run this script.
You will need kernel-devel package installed to compile drivers, installing this package should provoke you to install any other development tools required if they are not installed already.