Smartphones carrying Google’s Android operating system outsold the iPhone in the first quarter of 2010, according to new research out today from NPD.

During the quarter, Android handsets accounted for 28% of Smartphone sales, beating out iPhone OS and its 21% share. BlackBerry was the bestselling OS, with its devices capturing 36% of the market. NPD attributes the shift to strong sales of the Motorola Droid and Droid Eris.

The news follows a report last month from AdMob that showed Android’s share of the mobile OS market had actually grown past that of iPhone OS, at least in the U.S. Worldwide, iPhone OS still has a big lead, however, with 46% share compared to Android’s 25%. AdMob’s data is based on ad requests across mobile websites and applications.

With the new Droid Incredible reportedly selling quite well, this trend may continue in the near-term. However, the fourth-generation iPhone is expected to debut next month. Rumors that the iPhone will soon come to Verizon also continue to intensify, with that carrier’s customers indicating they are ready to welcome the device with open arms. If all of that happens, the numbers could quickly swing back in Apple’s favor. Stay tuned.