If the modem is a "Conexant HSF modem", you'll find that the new drivers are speed-locked to 14.4k ... BUT, you can download an older non-speed-locked version here
Just be warned that it doesn't seem to work with the 2.6 kernels, but if you're using Redhat 9.0 or less, it should
work. Just be prepared to shell out for a license to unlock the newer driver. I had to after upgrading to MDK10, but it's a good driver and I rarely get drop-outs or modem lock-ups like I used to get with the older driver.