20 Awesome resources to help you design and prototype your Windows Phone 7 apps

Microsoft Feed - 20 Free Prototyping, Mockup and Wireframing Resources for Windows Phone 7

"Here are 20 free prototyping, sketching, mockup and wireframing resources for Windows Phone which can be used to create application layouts, to help guide UI development, or to pitch an idea. Enjoy and Share!

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I think this one is my favorite  :)