According to the latest research figures, 31 percent of consumers who plan to get a new smartphone indicated Android was now their preferred OS.

Nielsen's monthly surveys of U.S. mobile consumers for January 2011 - March 2011 also show that Apple's iOS has slipped slightly in popularity to 30 percent and RIM Blackberry is down to 11 percent. Almost 20 percent of consumers are unsure of what to choose next.

This is the first time iPhone slips in the second place in consumers' smartphone choices. Nielsen's monthly surveys of U.S. mobile consumers from July-September 2010 had shown that consumers planning on getting a new smartphone had a clear preference: A third (33%) wanted an Apple iPhone. Slightly more than a quarter (26%) had said they desired a device with the Google Android operating system (OS). And 13 percent said they wanted a RIM Blackberry.

The new dynamics are already translating into sales, Nielsen said. Half of those surveyed in March 2011 who indicated they had purchased a smartphone in the past six months said they had chosen an Android device. A quarter of recent acquirers said they bought an iPhone and 15 percent said they had picked a Blackberry phone.

Which brings us to the installed base of smartphone consumers: As of March 2011, 37 percent of mobile consumers who owned a smartphone had a device with an Android OS. Apple's iOS, claimed by 27 percent of consumers, is now outpacing Blackberry, which has 22 percent of the market.