Excerpt from book:

Sometimes it becomes apparent that previous approaches to a problem haven’t quite worked the way you anticipated. Perhaps you just need to clear away the smoky residue of the past, take a deep breath, and try again with a new attitude and fresh ideas. In golf, it’s known as a “mulligan”; in schoolyard sports, it’s called a “do-over”; and in the computer industry, we say it’s a “reboot.”

A reboot is what Microsoft has initiated with its new approach to the mobile phone market. With its clean look, striking fonts, and new organizational paradigms, Microsoft Windows Phone 7 not only represents a break with the Windows Mobile past but also differentiates itself from other smartphones currently in the market. Windows Phone 7 devices will be made by several manufacturers and available with a variety of cell providers.

For programmers, Windows Phone 7 is also exciting, for it supports two popular and modern programming platforms: Silverlight and XNA.
Silverlight—a spinoff of the client-based Windows Presentation Foundation (WPF)—has already given Web programmers unprecedented power to develop sophisticated user interfaces with a mix of traditional controls, high-quality text, vector graphics, media, animation, and data binding that run on multiple platforms and browsers. Windows Phone 7 extends Silverlight to mobile devices.

XNA—the three letters stand for something like “XNA is Not an Acronym”—is Microsoft’s game platform supporting both 2D sprite-based and 3D graphics with a traditional game-loop architecture. Although XNA is mostly associated with writing games for the Xbox 360 console, developers can also use XNA to target the PC itself, as well as Microsoft’s classy audio player, the Zune HD.

Either Silverlight or XNA would make good sense as the sole application platform for the Windows Phone 7, but programmers have a choice. And this we call “an embarrassment of riches.”