What's wrong with the blank information of the unknown number?

Unknown number: One is that the other party has applied for a service that does not display the number, and the other is that the other party uses phones other than China Mobile, China Unicom, Telecom, Netcom and Tietong to make calls. These phones are network services of small companies, and these state-owned companies do not support displaying their numbers.

Blank SMS: error message, suddenly returned. But it has been sent to your mobile phone; The other is that others did it on purpose.