Are we talking all Android devices, or sales of one particular device?
Interesting side-note: Nokia 1100 sold 250 million units.
Yeah that gets slightly tricky with the somewhat disposable nature of phones/tablets/devices, potentially more so if people do actually install android on different things (so far I doubt that is a terribly high number but most of the things like the ouya and gamestick are not out yet) and that says nothing of not every android device being used even nominally playing games.