According to a report fresh out of IDC, Redmond’s Windows Phone operating system is destined to overtake iOS sometime by 2015. However, Google’s Android OS is expected to maintain its lead and outsell both WP and iOS.

Analysts expect Android will seize a 43.8 percent market share by 2015, while Windows Phone and iOS will trail with 20.3 and 16.9 percent respectively. The projections are rather optimistic, as Windows Phone is expected to end this year with a meagre 3.8 percent share.

Microsoft’s new mobile OS has been off to a rather rough start, but the long-term partnership with Nokia is expected to turn things around. Nokia’s Symbian OS will be all but dead by 2015, but it still commands a 20.6 percent share.

Overall, IDC beancounters expect smartphone shipments of nearly 1 billion units in 2015, about double the 472 million units expected to ship in 2011.

More here.