Facebook recently added a new feature for Messenger users. It is "video calling" feature. This feature is added for all app users, whether it is Android or iOS.
This feature is free for all app users and the main advantage of it is video calling can be done from Android user to iOS user and vice versa.
Messenger app will now show the video calling icon at the top of the app.
Check it, select the friend of your choice and tap on the video calling icon at the top and that's it. Enjoy the latest feature by Facebook.