Initiate call in Windows Phone 7

I am working on a Windows Phone 7 app and I want to give the option for the user to m开发者_高级运维ake a call. i.e How can I initiate a call when the user press a "call" button in my app? Looks like that API is not yet exposed.

The API you want is PhoneCallTask Note that many of the external actions your app can initiate are in the Microsoft.Phone.Tasks namespace.