Kantar, a researching firm has released a report showing iOS continues to be the top selling smartphone platform in the U.S. with a 51.2 percent market share for sales during the 12-week period ending on December 23, 2012.

Kantar found that Android dropped from 44.8 percent to 44.2 percent compared to the same data from the previous year. Windows Phone took the third position with a 2.6 percent market share.

The research firm also ranked the top carriers for the 12-week period and found AT&T continued its lead with 33.3 percent of smartphones sold during the period. Verizon followed in at a very close second with 32 percent of smartphones sold and Sprint came in third with 14.8 percent of smartphones sold.

Kantar also revealed some interesting statistics in its report. Kantar Worldpanel ComTech analyst Mary-Ann Parlato said:

"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.

"In particular, 36% of iOS sales were derived from other smartphone users over the last year. While this figure remains stable over time, the proportion of Android users moving towards the Apple brand increases. 19% of iOS sales over the last year were derived from Android users, compared to 9% in 2011.

"This trend is most evident within Verizon where half (49%) of iOS sales were derived from users of other smartphone brands, and 30% were derived from Android. These figures are much higher compared to AT&T where 15% of iPhone purchasers came from other smartphone users (6% from Android).

"While for other customer groups, 35% of iOS sales were those upgrading from a previous iPhone and 30% were those upgrading to their first smartphone."

The mobile world these days consists of two players - Apple and Google. It will be interesting to see if any of the upcoming new mobile operating systems like BlackBerry 10, Firefox OS, and Samsung's Tizen have any effect on the market and the two major players.