Facebook just pushed a major update to its Messenger software in the App Store. On iPhones with iOS 10, the app now takes advantage of Apple's new CallKit framework to make audio (VoIP) calls from Messenger look and behave like normal cellular calls with full support for Lock screen and Phone integration.
Bumped to version 89.0, the app now shows incoming VoIP calls from Messenger contacts right on your Lock screen complete with fullscreen contact images, standard controls like the Mute, Keypad, Speaker, Add Call and Video buttons and more.