Hudson Kimon Stack Overflow • Recommends
On “Implementation of WhatsApp/Telegram like calling feature in Flutter”
There is a great youtube series on this exact topic. In the series, a YouTuber by the name of the CS Guy creates a clone of Skype. I've placed the link to the video where he explains how to create a pop-up screen when a user calls another user, however, you may need to watch the previous videos within the series in order to get everything working. Its quite long but I recommend you watch the entire thing. In terms of displaying notifications when a user is called, I recommend you watch a video by Fireship listed below. In the video, he explains how to send notifications in the background when a certain event occurs in Firestore.
I can't explain the entire process in detail to achieve what…