How to check whether a mobile phone number is empty?

If I am right and want to know if the right mobile phone number is empty, I usually use the mobile phone number I am using to send a message to that number (I don't know if it is empty).

(The following two kinds of mobile phones should be available. As long as the other party's mobile phone is empty, the text message can't be sent naturally. )

If your mobile phone sends a short message prompting "delivery", then the other party's number is in use.

If the other party's number has been cancelled (or the number does not exist), sending SMS will display "undelivered".