When AT&T announced its quarterly results, the carrier revealed the iPhone was the top selling device on its network. In the first calendar quarter of this year, the AT&T network activated 5.5 million smartphones - 4.3 million of these devices were iPhones.

AT&T representatives have pointed out that iPhone sales were driven by "AT&T's 4G network, which lets iPhone 4S download three-times faster than other U.S. carriers' networks." After the latest iOS version was released, the carrier intensely informed its subscribers that iPhone 4S will benefit from its 4G networks.

AT&T confirmed that about a third of its customers enjoy 4G data speeds on their smartphones. 21 per cent of Apple smartphones sold on the AT&T network represent new activations, which means that new customers attracted to the carrier, bought an iPhone.

The first three months of 2012 were the best-selling quarter for AT&T. The rival carrier, Verizon Wireless, also reported that the iPhone is its top selling smartphone.

On Verizon networks, only 3.2 million iPhone 4 and iPhone 4S were sold in the FY 2012 Q1. In addition, iPhone didn't account for such a larger share, of 6.3 million Verizon's total activations.