AT&T says, effective Oct. 1, it will “throttle” the speed of users who have enjoyed unlimited data service on their smartphones, when they surpass a certain data limit.

The company cancelled its unlimited plans last year in response to the introduction of the iPhone 4, although it permitted existing unlimited plan-holders to keep them.

Now there appear to be some changes in this policy.

AT&T stated that the top five percent of data users on its network use up twelve times as much data as the average user.

Consequently, the company will place curbs on “unlimited” plan users who exceed a certain limit of data usage. As such, network speeds will be cut, although AT&T did not indicate specifically what the limits and speed reductions will be.

The company further assured that only a “very small minority” of its users will be impacted.

“This step will not apply to our 15 million smartphone customers on a tiered data plan or the vast majority of smartphone customers who still have unlimited data plans,” the company said in a statement.

According to reports, many more users will likely reach the data usage limits fairly soon as the company introduces its new 4G LTE network which has much faster data speeds that the current HSPA+ network does.