/usr/share at
Oh. I used to have a 2GB "unlimited" 3G plan for ~15US$/mo, and I only remember going over the limit (at which your speed is limited, but you don't pay any extra) once.
Of course, my mobile browsing habits were limited to text websites -- no music streaming, no YouTube or anything like that.
I never realised that. Most of the time I don't view media unless i'm at home, even though it is unlimited. If I go over 5GB (some cases 6.2GB), the speed is slowed down until the next billing cycle.