I tried to get Cingular to add the required "WIX" entries to my account, but they said they could not find them (talking to a "normal" customer support rep). Then, I talked with the Cingular Data Connect support folks, and they said that the BlackBerry device could not support modem connections (which I ignored) and that the WIX items are not in the billing system anymore. They said that this means they have dropped the "Pay per use" and you now have to buy a separate data plan. I went ahead and had them enter a 5MB data plan on my acct just to try it out (with the intent of cancelling it), but I still cannot get the connection to work. I am using all of the settings listed here, but I'm getting a 718 (PPP Timeout) error. :(
It makes me wish that I would have stayed with ATTWS a while back since it doesn't look like they have these problems.