Why can't I send short messages when I change my mobile phone to Unicom card? What happened?

If Unicom mobile phone users can't send short messages, they can try to restart or change their mobile phones to test whether there are any of the following situations:

1. The SMS center number is set incorrectly, please re-enter the correct SMS center number; 2. No signal or low battery; 3. Because the system is busy during the holiday short message sending peak period, it is suggested to try again later or avoid the sending peak period;

4. The sending format is incorrect. If you send a short message to PHS users, you need to add the area code before the number; 5. The short message sending time exceeds 24 hours; 6. The mobile phone shields the short message sending function; 7. Blacklisted by SMS; 8. Insufficient quantity balance; 9. SMS inbox and outbox are full.