Hello!
I installed FC3 with kernel 2.6.9 on my acer laptop and had same problem with the ltmodem.
I successfully installed my softmodem by downloading the ltmodem-8.31a10.tar.gz source file archive from
http://www.heby.de/ltmodem.
It is very simple to compile and it worked out at first try for me.
You have just to run some scripts:
./scanmodem #to check if modem is known
./build_module
./ltinst2
./autoload
Hope to be helpfull
Good luck!