Because Visual Studio 2010 does not support mobile application development for Windows Phone prior to Windows Phone OS 7.0, you cannot use the following features: .NET Compact Framework projects, Visual C++ device projects, smart device CAB projects, Device Emulator and Device Emulator Manager, testing tools for device projects, and Device Security Manager.

Mobile application development is still supported in earlier versions of Visual Studio, such as Visual Studio 2008.
Visual Studio also supports a different kind of device development known as Mobile Web development with ASP.NET. Mobile Web development refers to the development of mobile Web applications that run on a Web server and are rendered in different formats on a variety of browser-equipped mobile devices.