Call Control in Android

This tutorial is for those who want to control Phone Call in Android OS. Programmatic approach to Accept or Reject call without user intervention.

Kindly note, this approach uses Java Reflection to call methods of an internal class of Android Telephony Framework and might not work with all versions of Android OS. The core concept has been explained in this Android open code.

1st thing 1st, Give the permission.
You need to define 3 User Permissions to handle call related functionality-

• android.permission.READ_PHONE_STATE
• android.permission.MODIFY_PHONE_STATE (For answerRingingCall() method)
  
• android.permission.CALL_PHONE (For endCall() method)

Define a Receiver...
Create a Receiver which accepts broadcasts with intent action android.intent.action.PHONE_STATE, define following in the Manifest-
[receiver android:name=".PhoneCall"]
        [intent-filter]
            [action android:name="android.intent.action.PHONE_STATE"/]   
        [/intent-filter]
[/receiver]

Handle Broadcast inside your Receiver...
Override onReceive() method and using Java Reflection try to get the Instance of one of hidden class of Android Telephony Framework- com.android.internal.telephony.ITelephony
ITelephony defines a set of useful methods to control the Call state, which are hidden from general Android API.

private void getTeleService() {
        TelephonyManager tm = (TelephonyManager) context
                .getSystemService(Context.TELEPHONY_SERVICE);
        try {
            // Java reflection to gain access to TelephonyManager's
            // ITelephony getter
            Log.v(TAG, "Get getTeleService...");
            Class c = Class.forName(tm.getClass().getName());
            Method m = c.getDeclaredMethod("getITelephony");
            m.setAccessible(true);
            com.android.internal.telephony.ITelephony telephonyService = (ITelephony) m.invoke(tm);
        } catch (Exception e) {
            e.printStackTrace();
            Log.e(TAG,
                    "FATAL ERROR: could not connect to telephony subsystem");
            Log.e(TAG, "Exception object: " + e);
        }
}

Now, you can use telephonyService (which is an instance of com.android.internal.telephony.ITelephony) to "Accept"/ "Reject" call and many other operations.
// Accept Call
telephonyService.answerRingingCall();
// Reject Call
telephonyService.endCall();

Flow to create a Call blocking Application
1. Create option to add and store Phone Numbers to be Blocked
2. Read incoming phone number

String incommingNumber;
@Override
public void onReceive(Context context, Intent intent) {
    Bundle b = intent.getExtras();
    incommingNumber = b.getString(TelephonyManager.EXTRA_INCOMING_NUMBER);
    // Additional Step
    // Check whether this number matches with your defined Block List
    // If yes, Reject the Call
}

3. Reject this Call- telephonyService.endCall();

Hope this helps! I have developed one widget App (PhoneAway) following above mentioned concept, feel free to download source and explore.

Mute Call:
To mute an ongoing call, you can use com.android.internal.telephony.ITelephony.setMute(boolean ). You need to make sure the Call State is CALL_STATE_OFFHOOK. I couldn't test below code properly. Please let me know if the Mute functionality works.

if(tm.getCallState() == TelephonyManager.CALL_STATE_OFFHOOK){
  // mute the call
  telephonyService.setMute(true);
}