• by Mark Walsh  @markfwal, March 29, 2012

Half of U.S. mobile users now have a smartphone, according to new data from Nielsen. The 49.7% of mobile subscribers with a smartphone as of February is up from 36% in the year-earlier period, reflecting a 38% increase. Underscoring that growth rate, more than two-thirds who bought a new handset in the last three months chose a smartphone over a feature phone.

Nielsen’s estimate of smartphone penetration tends to be more aggressive than others. comScore, for instance, put that figure at 42% among U.S. mobile users, and a recent Pew report found that 46% of American adults owned a smartphone as of February. The Nielsen estimate is based on a survey of more than  20,000 mobile users.

When it comes to smartphone operating systems, Android maintains a commanding lead, with a 48% share of the market, followed by iOS at 32.1%. BlackBerry phones represented another 11.6%, down from 14.9% in December. Recent trends indicate that Apple is taking more share from BlackBerry and other competitors, including Microsoft’s Windows Phone platform.

Among people who purchased smartphones in the last three months, 48% surveyed in February chose an Android, and 43% chose an iPhone. Only 5% bought a BlackBerry, and 4% got another type of smartphone. Apple has gotten a big lift from the iPhone 4S, which helped it sell a record 37 million iPhones overall in the fourth quarter.

In December, 44.5% of new smartphone buyers got an iPhone, up from 25.1% in October. In February, the 48% who said they had bought an Android phone was up from 46.5% in December. Windows Phone could get a much-needed boost when AT&T launches Nokia’s Lumia 900 in April. The carrier is planning a major push behind the Windows Phone-powered smartphone, priced at $99.99.