iOS background apps

Obviously, WhatsApp iOS application is listing to an agreed upon port. If I don’t start the iOS app, it can’t listen for communication. If I have selected no background activity, it can’t run in the background

I think this is an example of an application that breaks the rules and it is running resident processes (probably at startup) without the user’s knowledge. Is there an iOS app that monitors the ports and can turn them off at will?

Thanks, very interesting completely different from how I thought it was implemented. Any how it begs the question, is a read receipt just a confirmation that it hit Apples notification server or actually a read receipt....

thanks again!

Little Snitch would be great for the iPhone