How to send a short message to a mobile phone in a nearby area in the Korean drama Ghost (without knowing the other party's number), its principle and implementation method thank you.

Query the mobile signal of a certain area through the server of network service provider (mobile, China Unicom, telecom, etc.). ), the numbers in this area can be found. But outside of them, it is impossible to find. . . . Isn't it common in movies to detect the position of this mobile phone through its signal? That's probably the case. ...