im still clueless, never had this many problems with dialup before, although Ive had my share of issues with it
temporarily, you may want to use somekind of generic dialer with a log, like wvdial for example so you can see whats happening, Id do this as a last resort, with something like ubuntu this will be an additional headache
also check the syslog and maybe even dmesg, there may be log activity of whats going on here too, you may be able to run your current dialer in console mode as well and maybe see some debugging info on it