Charles Petzold, veteran technical writer, is writing a book on developing for Windows Phone 7 and has released a 153 page draft ebook of the paper version coming this fall which covers:
Part I Getting Started
Chapter 1 Phone Hardware + Your Software
Chapter 2 Hello, Windows Phone
Part II Silverlight
Chapter 3 Code and XAML
Chapter 4 Presentation and Layout
Part III XNA
Chapter 5 Principles of Movement
Chapter 6 Textures and Sprites
You can download the ebook in XPS format here, in PDF format here and code samples for this draft preview are here.
Read more at Microsoft Press here.