Getting several different calls a day. Rings 2 times and hangs up. I have my police whistle ready and when I hear a voice I'm going to blast their eardrums. I'm sick, I'm tired, and I'm not going to take it anymore!
Its useless making a loud noise , such as a bullhorn or blowing a whistle , thinking it will hurt their ears or bother them enough to not call again. Sound begins to distort at high levels from your phone's microphone and is only as loud as the receiver's volume level. You will be the ONLY one who hears the full volume of such a stunt and might be damaging to your hearing, not theirs.
Here is an example to help you understand why it wouldn't work:
Take your camera and point it directly at the Sun and send the video to someone (or yourself) and it will ONLY display as brightly as the device's screen resolution allows, not as bright as the actual Sun. Sound works in the same manner on a phone or computer.