The phone number is empty, and the message can be sent?

That's the other party's call transfer ~ ~ ~ that's to transfer all calls to an empty number. Of course, you can set this number at will.

I've played before

The general steps are as follows

Settings → Call Settings → Call Transfer → There will be many options after entering. When you want to turn, you can choose which one to turn → Start → This depends on your own choice. I usually choose "Other Numbers" and then enter an empty phone number → OK.

enough ..............