Why can't Unicom send a short message?

The ways to deal with the failure of mobile phone to send short messages are as follows: 1. I suggest you change your mobile phone to see if you can send and receive short messages. 2. If you can send and receive short messages, I suggest you re-insert the card into your mobile phone and send yourself a short message to see if you can receive it. 3. If not, I suggest you check whether it is a sim card problem. 4. Check whether the SMS center number of the mobile phone is set correctly. 5. Bring your mobile phone card to the local business hall for testing or replacement.