How to tell whether the information sent by the other iPhone is ordinary information or iMessage information? It's each other's, not mine.

First of all, the other party already knows that you are using an apple. (The premise is that the other party also understands that "Apple and Apple will send messages in blue")

Then, if you close imessage, you won't receive the blue message, because this message will only be displayed if both parties open imessage.

Finally, even if imessage is turned off, you will receive a short message from the other party.

Because the function of "imessage" can also be said to be the function of sending messages to the other party for free, as long as both parties open imessage and display blue "Send" when sending messages, it means that the messages you send will not be charged. On the contrary, if you turn it off, it means that you need to pay for the messages you send.