Since android 2.3 Google has deleted –
<uses-permission android:name="android.permission.MODIFY_PHONE_STATE" />
http://code.google.com/p/android/issues/detail?id=54
But on Android telephones 2.3 and up to 4.0 – there is a function to “add phone to blocklist”. Is there any way to add phonenumber programatically to blacklist without using rejection of ITelephony.aidl?
Unfortunately, the only way to reject a call is to cut it. And the only way to cut it to use ITelephony.aidl.
Another way to switch the phone to airplane mode and back.
So you can design an app with a listener for incoming calls. Compare that incoming call phone number with a possible black listed database and then take an appropriate action on a match.