By 2015, IDC expects Windows Phone to be number 2 operating system worldwide behind Android with 20.9% market share from current 5.5%.

IDC Forecasts Worldwide Smartphone Market to Grow by Nearly 50% in 2011

"Android is poised to take over as the leading smartphone operating system in 2011 after racing into the number 2 position in 2010," said Ramon Llamas, senior research analyst with IDC's Mobile Devices Technology and Trends team. "For the vendors who made Android the cornerstone of their smartphone strategies, 2010 was the coming-out party. This year will see a coronation party as these same vendors broaden and deepen their portfolios to reach more customers, particularly first-time smartphone users."

Nokia's recent announcement to shift from Symbian to Windows Phone will have significant implications for the smartphone market going forward. "Up until the launch of Windows Phone 7 last year, Microsoft has steadily lost market share while other operating systems have brought forth new and appealing experiences," added Llamas. "The new alliance brings together Nokia's hardware capabilities and Windows Phone's differentiated platform. We expect the first devices to launch in 2012. By 2015, IDC expects Windows Phone to be number 2 operating system worldwide behind Android."