How to build WhatsApp like audio-video calling in Flutter using CallKit

In this tutorial, we learn how to build an audio and video-calling WhatsApp clone using Flutter. The key points of the text are as follows: 1. The calling functionality of WhatsApp is replicated in this demo, but not messaging and authorization. 2. Video/audio calling is accomplished using 100ms' Flutter SDK, while call notifications are instrumented using Firebase. 3. The project starts by cloning the hms-callkit-demo as a starter for this project. 4. A new directory called whatsapp_ui is created inside the lib folder of the Flutter project to create a WhatsApp Home Screen-like interface. 5. A flow is added to add users to the application, and Firebase is used to store the FCM token of the users. 6. The onPressed of the CustomButton on the login_page.dart is updated to store the FCM token and phone number to the Firestore. 7. A chats list is prepared to show on the WhatsAppScreen of the applications using a new file called chats_list.dart. 8. The ChatListScreen() is added on the WhatsAppScreen by modifying the body. 9. Finally, a ChatScreen is added to show individual chats and initiate video calls from there. 10. The app_router.dart is updated to configure Navigation in the application, and the initialRoute in main.dart is updated accordingly. 11. The complete code for this project is available on GitHub.