Half of all AT&T smartphones still iPhones

AT&T (s t) unveiled its quarterly earnings Thursday, and they show that the iPhone (s aapl) was a strong performer for the carrier during the three-month period ending Sept. 30. The iPhone, despite being significantly older than most other smartphone offerings, and despite early 2011 availability on Verizon (s vz) in the U.S., accounted for more than half of AT&T’s total smartphone sales for the quarter.

AT&T sold 4.8 million smartphones during the third quarter, which accounted for an impressive two-thirds of all post-paid sales. Android(s goog) device sales also more than doubled vs the year-ago quarter, and non-iPhone devices now account for nearly half of AT&T’s smartphone sales.

While the iPhone actually lost ground from the same time the previous year (5.2 million activations during the third quarter 2010), the fact that Apple’s 16-month old iPhone 4 and reduced-priced older models, could still show such high numbers this year vs last when the iPhone 4 would have been only a few months old is very impressive.

It’s also worth noting that the iPhone was still an AT&T exclusive in Sept. 2010, whereas this year, Verizon began selling the device in February. So, to recap, with the addition of another major U.S. carrier as competition, and with hardware that’s more than a year old, iPhone sales on AT&T only slid by 400,000 units. I can’t help but think the brand new iPhone 4S with both its hardware and software improvements could significantly slow the ability of non-iOS smartphones to play catch-up again next quarter.