Is there an augmented reality framework that works on iPhone, Android, and Windows Phone 7?

Question

I want to develop an application which runs on iPhone / Android / Windows Phone 7 smartphones and is able to recognize a marker and place augmented reality content on it.

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Answer 1

Not sure about Android or iPhone, but Kevin Marshall has done some proof-of-concept work on Windows Phone 7. You should keep in mind though, that augmented reality on WP7 requires access to camera APIs that are not publicly available and as such any AR application on WP7 would not be available officially through the Marketplace. Device manfacturers (such as LG) have access to these APIs, which is how some AR applications already exist for WP7.