PhoneStateReceiver.java

public class PhoneStateReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        // Check phone state
        String currentPhoneState = intent.getStringExtra(TelephonyManager.EXTRA_STATE);

        // If the phone is ringing
        if (currentPhoneState.equals(TelephonyManager.EXTRA_STATE_RINGING)) {
            // If the phone is already in a call, ignore this call.
            AudioManager audioManager = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
            switch (audioManager.getMode()) {
                case AudioManager.MODE_IN_CALL:
                    return;
                default:
                    break;
            }
        }

        // If we should intercept the call, send it off to the IntentService since this will take some time.
        context.startService(new Intent(context, PhoneAnswerIntentService.class));
    }
}