Well, there's little more I can offer from here at the moment, given that I'm on a Debian system; other than suggesting that you check that you're a member of the dialout, dip and tty groups, and turning up the volume to check for the usual 'click' as the computer opens up the port to the phone line. Finally, I'd open up a shell and run (as root)
tail -f /var/log/messages
to see if the log here can give any clues as to why it's failing.
Good luck !