How to send imaccege on Apple mobile phone?

Apple's mobile phone can only send short messages if the information is turned on in the settings.

Step: Set Message -iMessage, and then select On. Enter the normal SMS interface. If the other party has enabled iMessage, it will be automatically converted to iMessage, and the color is blue, which is different from the green of normal SMS. When using, the device must be in a networked state, and the receiver of the information is also a person who has enabled iMessage and is connected to the Internet.