For those complaining that we don't get unlimited data on our iPhone plans like the US has, AT&T will introduce throttling for their heaviest users, albiet to a rate that is quite sufficient for general usage of 256k. This is being brought in due to the congestion and overall network performance that users have experienced.

Verizon have already gone down this path earlier in the year, and Virgin will introduce it at the same time.

http://9to5mac.com/2011/07/28/att-to-implement-data-throttling-in-early-october-just-in-time-for-iphone-5/