Just go to "Shop Cingular" click "Rate Plans" , enter yoru Zip Code, and browse over to the "Data Plans" tab, and beside the 'Data Connect' there is a link to "BlackBerry Data Access" and it shows them..

Blackberry / 4MB / $39.99 / 4 MB / $0.01/KB - $0.40


Blackberry / Unlimited / $49.99 /Unlimited $0.0/KB - $0.40

but threw Cingular they are rated on your bill as 34.99 and 44.99.

Its really easy to add just call 1-866-CINGULAR tell then your info and tell them what BB data plan you want. If you already have Media Basic or Works take that off and ad the BB Plan, and if you want SMS(text messages) you can add 1000 for 9.99 and so on.. after they put all the info in you just turn off your phone for about 5min. turn it back on and boom all set..