This is what is confusing about this article anyway. You used to be able to run your VoIP application in the background all of the time. This has been closed fo

This is what is confusing about this article anyway. You used to be able to run your VoIP application in the background all of the time. This has been closed for longer. But WhatsApp and Facebook are really old apps, supporting pretty ancient versions of iOS (last time I checked). They might have inherited the capabilities back from the time it was the only way to have VoIP? The intended way VoIP application should work is using PushKit and CallKit to show a native call screen after receiving a special VoIP push notification message. Only when the user accepts the actual application will open. "Background App Refresh" is used for silent push notifications, which should be used to download content when the application is not running. It could be used to download images in messages ahead of time, though could be abused just as well. "Background App Refresh" is not a reliable way to deliver notifications to an application since they're dropped pretty easily.