Here you can find very valuable resource from Microsoft Press, including Programming Windows Phone 7, by Charles Petzold.

Free ebooks: Great content from Microsoft Press that won’t cost you a penny
http://blogs.msdn.com/b/microsoft_press/archive/2012/05/04/free-ebooks-great-content-from-microsoft-press-that-won-t-cost-you-a-penny.aspx

Enjoy :)

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AMB