You can use launchers and choosers to make your application interact with other applications that are built into Windows Phone 7. For example, you can enable your application to access phone contacts as well as built-in hardware such as the camera.
Launchers and choosers work in essentially the same way. However, whereas a launcher implies “fire-and-forget” functionality, a chooser may (but does not always) return data to your application. When you trigger either a launcher or a chooser, your application is temporarily suspended until either the launcher or chooser completes or the user interrupts the operation. This suspension is known as tombstoning, and it has debugging implications, as you'll see shortly.
One of the reasons launchers and choosers are so useful is that they can provide additional information when your application triggers them. For example, when sending an email, you can provide content for the email body, or when launching a web search, you can set the text to search for. This interactivity between applications is part of what makes the Windows Phone 7 user experience great: it allows you to build into and extend an integrated user experience.
All launchers and choosers are contained in the Microsoft.Phone.Task namespace. This namespace also contains some other types, such as event arguments, that support the available launchers and choosers.
A number of launchers and choosers are currently available to Windows Phone 7 developers, ...