I have a Conexant, but I don't use it. I'm currently using my 536ep. I never could get wvdial to do its thing either. Maybe it was just me. Try pppd/chat combo. It's not hard, and there's even a setup script for the whole thing:
and download pppsetup. If nothing else that will give you handy ppp-on, ppp-off script to link up the interface with. I like it because it only uses pppd and chat. You might want to symlink your modem device to /dev/modem if you didn't do that already, most things look there.
The setup scripts just fill out your /etc/ppp/options file for pppd, and make a chat script in /etc/ppp/. Looks like this running:
/usr/sbin/pppd -detach connect /usr/sbin/chat -v -f /etc/ppp/pppscript
When you want the link, you just do "ppp-on". "ppp-off" downs it again.
>ip addr show
20: ppp0: <POINTOPOINT,MULTICAST,NOARP,UP,10000> mtu 1500 qdisc pfifo_fast qlen 3 link/ppp inet 220.127.116.11 peer 18.104.22.168/32 scope global ppp0
On that same server there's a bunch of other ppp programs too. Probably what is happening is your ISP is using a method of auth you're not prepared for or using. Could be chap, pap, mschap, etc. Mine was pap.
# General configuration options for PPPD:
# speed 9600 +19200 38400 *57600 (nope -> )76800 (not supported? ->) 96000
# Uncomment the line below for more verbose error reporting:
# This may NOT work 9-15 is valid
# If you have a default route already, pppd may require the other side
# to authenticate itself, which most ISPs will not do. To work around this,
# uncomment the line below. Note that this may have negative side effects
# on system security if you allow PPP dialins. See the docs in /usr/doc/ppp*
# for more information.