我打电话的时候怎么不显示手机屏幕呢?

I have written an application which include a service running in the background, and a GUI that includes (amongst other things) the ability to make a call to a predefined number. Now- when the user presses the button to make the call- the call is made OK- and the screen changes to the phone's GUI. I'd rather the app stays in view and the phone isn't shown at all really- but I can live with it briefly showing. However, to return to the application, the user must manually click the "back button£" on the phone. I want this to happen immediately the call is ringing if at all possible. I have tried using the PhoneStateListener- which I am already using for something else (in the service part of the app)- but can't seem to detect the call being made, and then show the main screen again.I have written an application which include a s