data showing install base of different versions of iOS?

Does anyone have a chart 开发者_开发技巧showing which version of iOS people have installed on their phone?

I doubt Apple would release this data, however maybe an independent research firm might?

Ok I found the answer to my own question.

http://chitika.com/research/2011/61-of-ipads-already-running-ios-4-january-ios-and-android-os-breakdown/