AT&T raises high-speed data cap on grandfathered unlimited data users to 22GB from 5GB25
AT&T announced on its website today that those grandfathered into its Unlimited Data plans, will now face being throttled after consuming 22GB of data. Previously, just 5GB of data usage on the Unlimited Plan could have left an AT&T subscriber throttled. Keep in mind that with AT&T, throttling takes affect only in areas that are "congested." The carrier will send out an alert to those who have used 75% of the 22GB cap (16.5GB) to warn them.
If you want to save on your data usage, one of the easiest ways is to make sure that when you are home or away, you are connected to a Wi-Fi network. In fact, many stores and restaurants offer free Wi-Fi service. It doesn't take terribly long to check for a Wi-Fi connection on your phone or tablet whether you're at home, or out. It is well worth the effort to check.
source: AT&T via AndroidGuys