According to the latest forecast from IDC, smartphone sales are expected to decline to their first ever single digit growth. The fast growing markets have changed quite rapidly in a decline, and the mature markets are relying on replacement buyers. In those mature markets, the smartphone has to be significantly better than the previous model to help drive adoption, whereas, emerging markets are mostly about product and service price.
Android still rules the roost in sheer volumes, with Apple showing the best growth, even if in second place to Android, it lags behind in sheer numbers.
For developers, there are important forecasts. Knowing where to develop what application can make a success or failure.
Here's a link to some of the detail in the forecast.