Source: NPD Group / Consumer Tracking Service / Mobile Phone Track

The big shocker in today's report from the NPD Group market research firm is that Google's Android operating system surpassed Apple to take the No. 2 position in the U.S. in the first quarter, with 28 percent market share -- behind only Research in Motion's BlackBerry, at 36 percent.

The result shows just how much the mobile market is still up for grabs. Microsoft might take solace in that fact. However, the numbers also showed the Redmond company's Windows Mobile operating system dropping to No. 4 in the market, with 10 percent market share. That was down from 21 percent one year earlier, when Microsoft was still No. 2, ahead of Apple's iPhone, according to the NPD data.

Microsoft is hoping to reverse its fortunes with the release of its Windows Phone 7 operating system later this year.

In the NPD news release, analyst Ross Rubin said wireless carrier activity continued to play "a crucial role in determining smartphone market share," noting in particular that Verizon Wireless has expanded its buy-one-get-one-free offer to a broader set of phones. The firm said those promotions helped lead to strong sales of the Droid, Droid Eris and BlackBerry Curve.

Overall, Verizon Wireless captured percent of the U.S. smartphone market in the first quarter, behind AT&T at 32 percent, according to the NPD data. T-Mobile was third at 17 percent, followed by Sprint at 15 percent.