IDC explains that the recession is responsible for the shift in growth rates: "Last year's high market growth was due in part to pent-up demand from a challenging 2009, when many buyers held off on mobile phone purchases." So now that those reluctant consumers felt comfortable enough to buy smartphones in 2010, they will be less likely to do so in 2011.
In line with most analysts' predictions, IDC sees Android grabbing a vast lead by 2015 with 45.4% (from 39.5%). But somewhat surprisingly, they predict that Apple's iOS will slip to 15.3% (from 15.7%). Of course, they also see BlackBerry losing some ground, and Symbian obviously vanishing after it's no longer part of Nokia's lineup.
Their most interesting prediction, which mirrored that of one Ovum analyst, regarded Windows Phone 7. They see the combined Windows Phone 7 and Windows Mobile market share rising from 5.5% to 20.9% by 2015, making it the second largest smartphone OS. And they attribute this growth to Nokia's vast production capacity.
source: IDC via Bloomberg