How to send free information on Apple's mobile phone?

IMessage sends information to other iOS devices and Mac computers through wireless LAN or cellular mobile network connection, which is not included in the SMS package, so there is no charge, just networking.

Facetime is a voice and video chat function between Apple users, and iMessage is an instant chat function between Apple users, both of which are limited to the exchange of data between Apple users through the network. It is equivalent to the current WeChat, which uses network data to communicate without charging your phone bill, but operators may charge activation fees for opening these two functions, so this window will pop up frequently.

If you feel useless, you can completely turn off these two functions in the settings and information in FaceTime.

When sending a message, if the text bubble you send is blue, which proves that the other party is also using Apple's iMessage service, then the message you send is free; If your text bubble is green, it means that the other party has no iMessage service. To some extent, it means that the other party is not using an Apple phone, and your conversation is the legendary "short message".