How can I send a text message for free if I have a letter?

First of all, your mobile phone should be able to use a trusted client, and then your mobile phone has a traffic plan. The person you send the letter must be a friend you trust.

Meet the above three conditions, you use your mobile phone to send text messages to each other, which means it is free.

Sending letters on the computer is really free. As long as the other person and you are friends with each other, it won't cost you money to send messages by mail.

If you can only send letters by ordinary SMS (you need to collect money), when you open the chat window, there will be a small line to remind you.