> For example: If you stop using WhatsApp for example, nothing bad happens if you try to send messages another way. But if you stop using iMessage, then you can no longer send a normal SMS to someone with whom you've communicated before using iMessage. The Messages app will tell you, "You must enable iMessage to send this message", even if it's an SMS text message to a normal phone number! Why shouldn't that work? To be able to again send SMS text messages to someone you used to talk with is to disable iMessage of course, then sign out of Facetime (who could imagine that as a necessary step?), sign out of iCloud, reboot the iPhone, and wait some minutes to hours to days until you are "deregistered" from iMessage. I'm talking about the same phone with the same SIM chip. The problem can become much worse if you've switched phones or SIM card.

That’s simply not true. I just turned off iMessage and instantly switched to the Message app and sent a SMS to someone I have a iMessage chat with and it worked without any problems