More than 3.6 million smartphones running Microsoft’s operating system were sold to end users worldwide in the first quarter, according to data released this morning by the Gartner research firm.

However, only 1.6 million of those were running the new Windows Phone OS, the report says — which appears to mean that legacy Windows Mobile devices outstripped their successor for the quarter.

By comparison, Gartner shows more than 36 million Android smartphones sold in the quarter, 27.6 million Symbian devices, and 16.9 million iPhones.

Windows Phone was originally hampered by its availability on only two of the four major U.S. carriers, AT&T and T-Mobile. Sprint came aboard in March and the situation will continue to improve with the upcoming release of the first Windows Phone for Verizon. (Note: Info about carriers corrected since original post; thanks to Josh in the comments.) Microsoft will release new details next week about the next Windows Phone version.

Gartner and IDC have both predicted that Windows Phone will surge in the coming years as a result of Microsoft’s partnership with Nokia. The first Nokia devices running Windows Phone are due on the market in 2012. Here’s the full Gartner chart showing mobile OS market share for the first quarter.

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