I own a TravelMate 653. And here we go: Install the kernel development packages (you need this to compile the driver).
Download the newest (2.9.9) driver: http://linmodems.technion.ac.il/packages/smartlink/
Unpack it and (please) read the README. Follow the instructions.
Copy the slmodem script to /etc/init.d
Activate it for runlevel 5 (graphical environment) using: RedHat Menu -> System Configuration -> Server -> Services (Maybe you have to insert a service "slmodem" first by using the menu).
Add a modem based network connection using the Fedora "Internet Configuration Wizard". Make sure you use /dev/SLtty0. Now we should be ready... You can activate it even from the command line "ifup ppp0" (if this is the name) - it's like a network device.
Personally, I use the "Modem lights" applet by Gnome to activate and deactivate the modem connection (It's faster than using the Fedora "Network Control" program.) Please make sure you set the lock file from ttyS0 to ttySL0 - otherwise it's not possible to dial. If you have an account named otherwise than ppp0 than change it accordingly.
PS: Sorry I'm not sure if all these steps are right, I'm at work.