Why are iMessage and iPhone SMS or SMS turned on in the settings?

First, both parties are Apple phones, and both of them have the iMessage function, which can be activated. In this case, iMessage can be used to send short messages or pictures. The content of the message sent is blue, and the message header is iMessage, as shown in the figure below. If it is ordinary information, the header is information;

2. Both parties are Apple phones. If either party does not turn on or activate the iMessage function, it cannot send.

IMessage information can only be compared with the general information of the original operator. The information sent at this time is charged, and the picture is sent by MMS. If the sender uses iMessage, the word "undelivered" will appear, indicating that sending iMessage information failed. If you click "Try Again" or "Send SMS", you will be charged for sending SMS. The watermark in the input box will also become "SMS/MMS", as shown in the figure below.