How to close Apple's 4s iMessage? Why don't you need to charge?

Open Settings-Information -iMessage and click Close.

After closing iMessage, there will be no more charges.

In the process of using iMessage, network traffic is used. If the transmission of iMessage fails, it will be automatically sent as SMS/MMS, and the charging standard is the same as that of ordinary SMS/MMS.

(Here's an extra tip about sending and receiving options when using iMessage. Choosing the phone number on your phone and the apple id on other ios devices can avoid you receiving duplicate messages. )