This is wrong. Before you type a message it says “iMessage” or “SMS” or “RCS” in the text field so you know what you are sending. If a message doesn’t initial

This is wrong. Before you type a message it says “iMessage” or “SMS” or “RCS” in the text field so you know what you are sending. If a message doesn’t initially go through first as iMessage then it tries to send it as SMS but you can disable the “Send as text message” in the Settings app on your phone if you don’t want your phone to do this.