No need to edit /etc/wvdial.conf except for user name, phone number, and password. Have you run the command wvdialconf? Can it find your modem?
Usually you get the "cannot open /dev/modem device ..." message because you dial up with wvdial using normal user account. You should use root account to dial up using wvdial.
Take a look at this:
and this one
hsf modem. maybe a winmodem since it is in limodem website. Have you installed any driver for the modem?