Detecting an incoming call coming to an Android device. Remember to set the appropriate permissions in AndroidManifest.xml as suggested in the Stackoverflow link. Usage example in comments. Source: Gabe Sechan http://stackoverflow.com/a/15564021/264619 Explanation: http://gabesechansoftware.com/is-the-phone-ringing/#more-8

PhonecallReceiver.java

package com.gabesechan.android.reusable.receivers;

import java.util.Date;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.telephony.TelephonyManager;

public abstract class PhonecallReceiver extends BroadcastReceiver {

    //The receiver will be recreated whenever android feels like it.  We need a static variable to remember data between instantiations

    private static int lastState = TelephonyManager.CALL_STATE_IDLE;
    private static Date callStartTime;
    private static boolean isIncoming;
    private static String savedNumber;  //because the passed incoming is only valid in ringing


    @Override
    public void onReceive(Context context, Intent intent) {

        //We listen to two intents.  The new outgoing call only tells us of an outgoing call.  We use it to get the number.
        if (intent.getAction().equals("android.intent.action.NEW_OUTGOING_CALL")) {
            savedNumber = intent.getExtras().getString("android.intent.extra.PHONE_NUMBER");
        }
        else{
            String stateStr = intent.getExtras().getString(TelephonyManager.EXTRA_STATE);
            String number = intent.getExtras().getString(TelephonyManager.EXTRA_INCOMING_NUMBER);
            int state = 0;
            if(stateStr.equals(TelephonyManager.EXTRA_STATE_IDLE)){
                state = TelephonyManager.CALL_STATE_IDLE;
            }
            else if(stateStr.equals(TelephonyManager.EXTRA_STATE_OFFHOOK)){
                state = TelephonyManager.CALL_STATE_OFFHOOK;
            }
            else if(stateStr.equals(TelephonyManager.EXTRA_STATE_RINGING)){
                state = TelephonyManager.CALL_STATE_RINGING;
            }


            onCallStateChanged(context, state, number);
        }
    }

    //Derived classes should override these to respond to specific events of interest
    protected void onIncomingCallStarted(Context ctx, String number, Date start){}
    protected void onOutgoingCallStarted(Context ctx, String number, Date start){}
    protected void onIncomingCallEnded(Context ctx, String number, Date start, Date end){}
    protected void onOutgoingCallEnded(Context ctx, String number, Date start, Date end){}
    protected void onMissedCall(Context ctx, String number, Date start){}

    //Deals with actual events

    //Incoming call-  goes from IDLE to RINGING when it rings, to OFFHOOK when it's answered, to IDLE when its hung up
    //Outgoing call-  goes from IDLE to OFFHOOK when it dials out, to IDLE when hung up
    public void onCallStateChanged(Context context, int state, String number) {
        if(lastState == state){
            //No change, debounce extras
            return;
        }
        switch (state) {
            case TelephonyManager.CALL_STATE_RINGING:
                isIncoming = true;
                callStartTime = new Date();
                savedNumber = number;
                onIncomingCallStarted(context, number, callStartTime);
                break;
            case TelephonyManager.CALL_STATE_OFFHOOK:
                //Transition of ringing->offhook are pickups of incoming calls.  Nothing done on them
                if(lastState != TelephonyManager.CALL_STATE_RINGING){
                    isIncoming = false;
                    callStartTime = new Date();
                    onOutgoingCallStarted(context, savedNumber, callStartTime);                     
                }
                break;
            case TelephonyManager.CALL_STATE_IDLE:
                //Went to idle-  this is the end of a call.  What type depends on previous state(s)
                if(lastState == TelephonyManager.CALL_STATE_RINGING){
                    //Ring but no pickup-  a miss
                    onMissedCall(context, savedNumber, callStartTime);
                }
                else if(isIncoming){
                    onIncomingCallEnded(context, savedNumber, callStartTime, new Date());                       
                }
                else{
                    onOutgoingCallEnded(context, savedNumber, callStartTime, new Date());                                               
                }
                break;
        }
        lastState = state;
    }
}

Regarding changes makes on Android Pie, (See https://developer.android.com/about/versions/pie/android-9.0-changes-all#restrict-access-phone-numbers),

You must replace lines 28 - 42 by

TelephonyManager telephony = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
telephony.listen(new PhoneStateListener() {
     @Override
     public void onCallStateChanged(int state, String phoneNumber) {
          onCustomCallStateChanged(context, state, phoneNumber);
     }
}, PhoneStateListener.LISTEN_CALL_STATE);

And rename onCallStateChanged() method in PhonecallReceiver class by onCustomCallStateChanged()

Thank you

Works all good just give these permissions and ask from user in an activity
android.permission.PROCESS_OUTGOING_CALLS
android.permission.READ_CALL_LOG
android.permission.READ_PHONE_STATE

Also, android.permission.READ_CALL_LOG is used to get phone numbers too no change in code Enjoy

for voip, if you are not using mode in_communication then use this to check if voip app in incoming : https://developer.android.com/reference/android/media/AudioManager.html#MODE_IN_COMMUNICATION