Try this first. This is how I got my PCI modem to work.

Type this into a root shell:
cd /dev
./MAKEDEV ttyS4
ln -s ttyS4 modem
chmod 777 modem
chmod 777 ttyS4

This will set up your default modem to run on ttyS4. For Win/DOS users ttyS4 is com5. This is an unusual com that is sometimes used by modems.

Hope that helps