While AT&T unlimited data plans are unlimited, data speeds are reduced for heavy users. AT&T recommends that users with unlimited data plans avoid downloading more than 3 gigabytes of data over 3G or 4G connections on the AT&T network in a month to avoid reduced speeds, as of March 2015.
Most cell phone companies reduce the network speeds for heavy users of their unlimited data plans, a procedure known as throttling. However, many customers have claimed that AT&T engages in throttling much more so than other cell phone providers and at much lower usage levels. In 2014, the Federal Trade Commission issued a complaint alleging that AT&T may have throttled users in large urban areas for using as little as 2 gigabytes of data in a month. The complaint also alleges that AT&T throttled up to 25 percent of its unlimited data plan users, as opposed to the 5 percent of the heaviest users on other networks that were subject to data speed limitations.
While AT&T's 3 gigabyte throttling threshold holds for users on 3G and 4G networks, AT&T is more generous to users of 4G LTE smartphones. AT&T recommends owners of 4G LTE phones use less than 5 gigabytes of data per month to avoid throttling.