I don't know much about FC4 (I did have FC2 a while back).
You are using wvdial to connect. Are you using a fancy graphical frontend (interface) or are you using a terminal and typing
If you are not using a graphical front end, can you post the last ~10 lines (remove phone number, user name if need be).
If the modem is connecting properly you might have to (re)install ppp and DHCP.