Andrew:
Setup your modem through system-config-network.
That's (essentially) what I did - except that I did it thru the menu (System > Admin).
Then from the command line issue 'ifup' to start the connection, ifdown to close the connection. Do it as your user id, not as root. The problem I had was I started the ppp connection as root and started my browser as user. You could also use "modem lights" to start the connection by changing the command it issues to ifup and ifdown.
That's exactly how I had it running (back in F6)! But it won't work like that now. :(
I also made changes to wvdial, but I discovered it was unnecessary.
What 'sections' does wvdial need in its conf file? I.e., does it need [dialer defaults]? [modem0]? [dialer (config name)]?