AT&T is apparently making good on its promise to cut back on speeds for heavy data users.

Posted by tech enthusiast site CultofMac, a text message sent by AT&T to such a user says that "Your data usage is among the top 5 percent of users. Data speeds for the rest of your current bill cycle may be reduced."

The data restriction policy comes as no surprise. AT&T had announced back in July that it would throttle speeds for heavy data users starting on October 1. The policy affects only subscribers who still have an unlimited data plan. Those with limited data plans who go over their allotment are simply charged for the extra data.

AT&T has not made it clear how much data you'd need to gobble up to appear in the top 5 percent, but the carrier has said that such users consume around 12 times more data than the average customer.

Responding to CNET's request for comment, an AT&T spokesperson promised to provide further details on its data policy.

News that the policy is being implemented comes at a time when AT&T is seeing increased sales thanks in large part to the iPhone 4S. The company announced yesterday that it expects to reach a new record of more than 6.1 million smartphones sold in the fourth quarter. AT&T activated more than 1 million new iPhones in just the first five days of the device's launch in October.

The company isn't just counting on the iPhone to boost business. AT&T just released its latest 4G LTE Android phone, the LG Nitro HD, as it tries to build up its LTE network.

But as business rises, so does data usage. J.P. Morgan estimates that the average iPhone user will consume around 800MB of data per month. That's not far off from the average non-iPhone user projected to grab around 825MB each month.

AT&T has itself been dinged in the past for its slow and sporadic network performance, especially among iPhone users. Though it's struggled to improve its network over time, the company still seems to be facing an uphill battle, certainly in terms of customer service and customer perception.

It was recently rated the worst cell phone carrier for the second year in a row by Consumer Reports. And earlier this year, it ranked at the bottom among all carriers in a survey conducted by J.D. Power and Associates.