Whether you’re familiar with, or new to, Silverlight and XNA Game Studio programming, Windows Phone SDK 7.1 provides the tools necessary to target Windows Phone users using either Windows Phone 7 or 7.5 devices and includes productivity enhancements such as an app profiler and an improved emulator. It also includes Microsoft Advertising SDK for Windows Phone.

URL: http://www.microsoft.com/visualstudio/en-us/products/2010-editions/windows-phone-developer-tools

Windows Phone applications
    

     The familiar powerful and easy to use Visual Studio integrated development environment (IDE) for building your Windows Phone app.

Windows Phone Emulator
    

     Once you’re built your app, test it using the Windows Phone Emulator. You’ll see it the way users will see it. Windows Phone SDK 7.1 includes an improved Windows Phone Emulator.

Windows Phone project templates
    

     Utilize any of the seven Windows Phone project templates to get a head start on design and development.

Expression Blend SDK for Windows Phone
    

     Seamless integration with Expression Blend means you can create unique and compelling apps that will shine in the Windows Phone Marketplace