If you are an iPhone user on a grandfathered unlimited data plan with AT&T, be careful how much data you use. You won’t get charged extra for using too much, but you will see your speeds drop from 3G to 2G. This only applies to the top five percent of data users, but it is still pretty ridiculous. If you are in that group, you will receive a text message telling you that your data is being throttled.
This sets a dangerous precedent for cell phone carriers. They offer unlimited data, but punish the users that actually make use of it to the fullest extent. The reports of this first came out in October, but it seems as though AT&T is finally taking action in a more visible way. AT&T claims this is more targeted at jailbreakers, but the fact is, regular users could easily hit high amounts of data without jailbreaking their phone.
At this point, it is unknown whether other US carriers will follow their lead, but now that the anger is already directed at AT&T for being the first, it would certainly be easier for others to follow.
If you are a high data user, try to be more cautious, as the last thing you want is to see your speeds drop considerably.
Source: Cult of Mac