Android still owns the U.S. market when it comes to smartphone operating systems, but Apple's iOS was able to win back losses in the most recent quarter, according to the latest research from Nielsen.

Nielsen says that 44.5% of consumers who purchased a smartphone in the last three months bought an iPhone. That number stood at 25.1% in the three months prior to the iPhone 4S's October launch. Further, of those who bought iPhones, 57% bought the iPhone 4S. (When the iPhone 4S launched, Apple cut the price of the iPhone 4 to $99 and the price of the iPhone 3GS to free.)

Overall, Google's Android holds a commanding lead over Apple's iOS, with 46.3% of all U.S. smartphone users owning an Android device. Apple's iOS earns about 30% of the market, according to Nielsen, or about two-thirds of Android's share.

Much of Apple's success in this most recent three-month period is no doubt due to the pent-up demand for the iPhone 4S (nee, iPhone 5). Apple debuted the smartphone four months later than the expected June 2011 launch. Verizon Wireless, for example, sold 4.2 million iPhones in the fourth quarter of 2011, more than doubling its iPhone 4 sales from the third quarter.

Looking at the rest of the field, RIM's BlackBerry platform sits in third place with 14.9% of the market. It decreased, but not by much. Nielsen didn't differentiate between versions of RIM's smartphone platform (BB7, BB6, BB5, etc.). BB7 hit the market in August with a new crop of BlackBerries, including the Torch 9810, the Bold 9900/9930, and the Curve 96xx series.

What about Microsoft's Windows Phone 7 platform? The legacy Windows Mobile 5.x/6.x platform owns 4.6% of the U.S. smart device market. That's Microsoft's old smartphone platform. In comparison, Microsoft's new Windows Phone 7 platform holds a meager 1.3% of the U.S. smartphone market. It falls behind even Nokia's Symbian and HP's webOS, each of which earned 1.4% of the market.

WinMo's continued large presence can likely be attributed to the hefty number of enterprise assistants/handhelds still being sold.

Comparing smartphones to feature phones in the U.S. market, smartphones have grown to 46% of the market, but the rate of growth is accelerating. Nielsen said "60% of those who said they got a new device within the last three months chose a smartphone over a feature phone."