I don't believe Cingular offers the Internet Browsing Service by default on BlackBerry Web Client accounts....to quote one of Marks FAQ's...
Cingular works now, though you may have to call Cingular to make sure that you ask for the "Data Connect" plan added in addition to your existing "BlackBerry Unlimited Data". Both data plans are required simultaneously. Once this is done, you will have several additional line items that show up on your Cingular bill.
If you are not sure if you have it, you can log into your Web Client account, and under profiles at the very bottom will be a second button to send a service book. Alternatively, you can look on the handheld itself. If you go into options -> service book, you are looking for an entry with [IPPP]...usually either "BlackBerry Internet Browsing Service [IPPP]" or "IPPP for BIBS [IPPP]"