Can anyone tell me how I can figure out whether to go with a limited or unlimited data plan? My new BB 9780 is on its way and I will need to make a decision about adding data to my account.

How does T-Mobile specifically count one's data usage and what is considered typical (I know the use of the word typical is problematic but I use that for lack of a better word)?

Does anyone know anything about some type of upcoming sale/special related to plans for TMobile that include data? I felt like I read something very recently about TMobile having some type of holiday special in early December but now I can't relocate the info.