How to send short messages cheaply?

If it is a smart phone, you can download Fetion, so you can send short messages through traffic. If you have WIFI around you, you don't even need traffic, and you don't need SMS fees. At the same time, if you have a computer, you can install a Fetion on the computer and add the mobile phone number of the person you want to send a message to. It is free to send information on the computer by fetion.