Apple's iPhone continues to be a big winner for AT&T.

In announcing its third-quarter earnings today, AT&T said that it activated more than 8 million smartphones over the past quarter, and a hefty 5.2 million of those devices were iPhones--"the most iPhone activations ever in a quarter," the carrier said. During the second quarter of 2010, AT&T activated 3.2 million iPhones.

The latest version of Apple's smartphone, the iPhone 4, went on sale just days before the start of the third quarter. Earlier this week, in reporting on its most recent fiscal quarter, Apple said that worldwide sales of the iPhone doubled from the same period a year earlier.

AT&T said that nearly one-quarter of all iPhone activations during the third quarter, which ended Sept. 30, came from new customers.

Beyond that, 57.3 percent of the company's "postpaid subscribers" have a smartphone. A year ago, that figure stood at just 42 percent. The company also added 2.6 million net subscribers, pushing its total to 92.8 million.

Data is helping drive revenue growth at AT&T. The company said that its data revenue grew by 30.5 percent to $4.8 billion during the last quarter.

All told, AT&T generated a $12.3 billion profit on $31.6 billion of revenue.