I had tzones from T-Mobile origionaly thinking that would work,since I got the bb unlocked and just used my existing sim. (previously the 4.99 tzones would give full html since I ran it trough a proxy, apperently the blackberry wont do that) - quickly learned that I needed the 19.99 blackberry internet addon to do anything.
So then I just shelled out for that, adds about 15 dollars to the monthly bill but a blackberry without internet access doesn't make any logical sence to me. That and 19.99 for unlimited didn't seem to bad compared to (edit: other companies [than T-Mobile].)
Edit: Incase your looking on T-Mobile's site; they only list the data plans seperately from a voice plan... So it'll say 29.99; To get data for 19.99 you appernetly need a voice plan. (see: http://www.geocities.com/andrebsd/bberry/tmobile.jpg for screenshot of my plan & services page)