Came across this image when I was surfing and I am thrilled to see Android's steady and massive growth. A definite explanation to such growth is the fact that Android phones are manufactured by many companies (in contrast to iPhone only by Apple) and there are many low-budget devices running it.
iOS certainly doesn't seem to catch up and I am baffled as to why. Although it had some issues with the battery, iPhone 4S was a massive success (or so I heard).
I badly want Windows Phone 7 to catch up! Although I am an Android fan, the beauty and simplicity of Windows Phone 7's interface has got me hooked up. And according to GSMArena, we are going to see cheaper WP7 phones introduced at MWC this year at Barcelona. That is a good sign! Not everyone can spend an year's salary on a phone.