Well, I got it to work with the help of a Cingular tech. rep.
The only change to any of the information posted here was the advanced modem init. string. I was told to use: AT+cgdcont=1,"IP","proxy"
I don't think that I've seen that string posted here before. I was still using the WAP@ sign-on and password. When I used the init. string posted here all I got was a 734 error.
There is also a special number at Cingular that deals with Blackberries and "data" related stuff. the number is: 800-552-3373. Note, that these are not the guys that helped me get it working. I was referred to them only when I started asking about billing. One of their automated options is even about using a Blackberry as a modem - I almost fell out of my chair when I got to that one!!
They said that even with an Unlimited Data plan, using the Blackberry as a laptop modem wouldn't be covered and each Kbyte would be billable. They also said that there wasn't a plan that covered use of the blackberry as a modem and they had no plans to create one. Now, they also said that even though it was billable it probably woudn't show up on your account as a charge, but "may" in the future. How's that for a specific answer? I've talked with over 6 different people/groups/supervisors at Cingular now about this and this guy/group is the only one that thinks that the modem use isn't covered under the unlimited data plan, but that they just don't happen to be actually billing it right now. They were very nice and offered to sell me an additonal plan to use a card in the laptop for an additonal $79 a month, however. Thank you for using Cingular...
Hope that this helps somebody. Thanks for all of the help here!!!