IDC on Tuesday posted the results of its new Worldwide Quarterly Mobile Phone Tracker report. Among IDC’s prognostications is that Windows Phone 7 will overtake iOS, thanks to Nokia.

[ad#Google Adsense 300×250 in story]In February Nokia announced plans to make Windows Phone 7 its primary smartphone strategy. Nokia’s decision to support Windows Phone 7 will have long-term repercussions that will benefit Windows Phone 7, according to Llamas, who expects to see Nokia-branded Windows Phone 7 devices in 2012.

“The new alliance brings together Nokia’s hardware capabilities and Windows Phone’s differentiated platform … By 2015, IDC expects Windows Phone to be number 2 operating system worldwide behind Android.”

The company predicts the global smartphone market will grow by almost 50 percent in 2011. IDC projects that more than 450 million smartphones will be shipped this year, compared to 303.4 million for 2010. IDC also projects that the smartphone market will grown more than four times faster than the overall mobile phone market.

Android will be the leading smartphone operating system in 2011, opines Ramon Llamas, senior research analyst at IDC. “For the vendors who made Android the cornerstone of their smartphone strategies, 2010 was the coming-out party,” he said.

IDC expects Android phones to occupy 39.5 percent of the 2011 smartphone market. Smartphones based on Symbian (the operating system still heavily leveraged on Nokia’s devices) occupy second place at 20.9 percent, with iOS coming in third at 15.7 percent. RIM’s BlackBerry smartphones will grab 14.9 percent of the 2011 market, according to IDC, with Windows Phone 7 bringing up the rear at a scant 5.5 percent.