Why is the SMS number received by the mobile phone unknown?

1, if the other party turns on the function of "prohibiting the other party from displaying the number", you will not display the number of the incoming call when you answer the phone, and the level of this function takes precedence over the function of "caller ID";

2. Dial through VoIP without displaying the number;

3. Use the service that can set the virtual number, and display the virtual number instead of the real number.