What's the difference between Xiaomi's short message and Internet short message?

Network SMS is when both parties are in wifi. If the other party is also a Xiaomi mobile phone, you can send a short message for free, which is not included in your short message package.

It's complicated to say. Actually, you don't have to worry at all. Turn on this function and it will recognize itself. You can send text messages normally without doing anything special. Those who meet the conditions of free SMS are automatically free.