Alternative call-screen

I'm developing an alternative call-screen for Android 2.1.

I thought, when I set a call directly in com.android.internal.telephony.ITelephony no android call-screen will appear, but I was wrong.

How can I manage to make开发者_如何学JAVA the default android call-screen disappear?

Thanks Flo

p.s. I know that com.android.internal.telephony.ITelephony is a private class and I know the risks.