Gartner predicts Windows Phone 7 will overtake Apple's iPhone in market share and being number two behind Android by 2015:
This prediction coincides with IDC's own prediction which also find Windows Phone 7 going past iOS and being the second most popular OS by 2015.
While many look at these figures with disbelief, the predictions do make sense. Unless Apple releases a cheaper iPhone it looks like their market share has plateaued. Apple iPhone market share is already amazingly high, with almost 1-in-6 smartphones being an iPhone. You have to consider that Apple does not have any mid-level or budget offering.
As for Windows Phone 7, it does not carry any of the baggage of the Windows desktop operating system. Windows Phone 7 runs fast and has a truly evolutionary Metro user interface. It slow adoption is really because it launched into a market with two established competitors. Had it launched a year earlier, things might have been different. Also like, Apple's iOS there are no mid-level and budget Windows Phone 7 units. As 1GHz processor make the transition from high end to mid-level phones you should see Windows Phone 7 market share increase.
The partnership with Nokia will boost Windows Phone 7 sales too. While you wont see Nokia Windows Phone 7 devices in quantity till 2012, one should not discount that fact the many Nokia buyers do not buy it because of the operating system, but simply because it is a Nokia. If only one in four Nokia buyers moves from Nokia-Symbian to Nokia-WP7, Windows Phone 7 will be a serious player by 2012. A predicting what will happen in 2015... that seems a bit too long in the smartphone market.