I also was throttled after 2 GB. It has been VERY frustrating to deal with because the throttling is INCREDIBLY slow. I am on the unlimited data plan. If my data is slow because of natural congestion then no one is limiting it, thus it is unlimited, and slow. However, if AT&T is limiting my data speed, then it is NOT unlimited.
Moreover, their contract (AT&T) says that they have the right to throttle if you are abusing the network by doing things they do not permit (they have a list of things) and/or if you are compromising the integrity of the network.
I know from first hand experience (they throttled me last month) that they are being malicious and attempting to force people out of their unlimited data plans (or they miscalculated and are making reasonable users [like me] very upset):
a) The speed you are throttled to is too slow to load webpages and other simple internet content. Often you have to reload. AT&T's full speed on an iPhone 4S in Sacramento is 3.5 Mbps. They have throttled me down to about 0.10 Mbps, about 2-3% of the normal speed.
b) I do not abuse the network. I watch half an hour of video during my lunch break at work. That adds up to about 4 GB a month.
c) I was throttled after using 2GB of data in 15 days. This is not compromising their network because they offer a 5GB plan.
d) The point in which you are throttled is a floating, regional rule. If few people in your region do more than check their email, or if they are always in Wi-Fi, you are suddenly an "abusive" user. There will always be a top 5%.
e) It does nothing for other users. I have streamed like this during lunch for a long time. It has always been fast. When testing the speed on friends' phones, they reach the speeds I have always gotten, even though a full 5% of AT&T's "data hogs" have been throttled down.
f) Finally, network congestion doesn't happen by the GB. It happens during congested TIMES. A more sensible policy would be to limit users data who access it at highly congested times. The logical error there is: this already happens, that's what network congestion is, many people get on at the same time, and the network slows down. Think of rush-hour traffic. Just because 1 car drove across the country doesn't mean that they are the cause for slow traffic speeds at 6pm.
Enough said. I'm pretty sure there is a class action lawsuit sitting on the table here...
Take care,
Mr. Frustrated