A new Gartner report about the mobile market came out a few days ago. From the data available from the press release announcing it, I made a graph about how sales by OS changed from third quarter 2009.
Short story is: Android went from 3.5% to 25.5% at expense of others OSs, Symbian in particular. Click on the image to see it larger.

Sales to end users change from Q32009 to Q32010 by OS

Sales to end users change from Q32009 to Q32010 by OS

francesco mapelli