The iPhone is still as attractive as ever — in large part because of adopted Android users — according to a new study released today by Kantar

During the 12-week period ending Dec. 23, 2012, iOS maintained its lead atop the U.S. smartphone rankings with 51.2 percent of market sales. That’s an increase of more than six percent from the same period in 2011.

Kantar analyst Mary-Ann Parlato credited Apple’s success to smartphone users jumping from competitors and buying the iPhone this year. She said 36 percent of iOS sales were derived from other smartphone users and 19 percent of those sales came from Android users. That’s compared to nine percent in 2011.

“Apple’s continual improvement is thanks to both the iPhone 5 and older models attracting various customer groups, from repeat Apple buyers, first time smartphone buyers and those coming from other smartphone brands,” she said in a press release.

Windows saw a slight increase from 2.2 percent in 2011 to 2.6 percent last year.

AT&T, meanwhile, also kept up its lead in the carrier competition with 33.3 percent of smartphones sold during the 12-week period, though Verizon was close behind at 32 percent.

With both AT&T and Verizon, the number of people using iOS increased while Android users decreased. 55 percent of AT&T’s iOS sales came from users upgrading to a newer iPhone.

Previously on GeekWire: Windows Phone Diary: So long Lumia 920, hello HTC 8X

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