When you use that air horn all you are doing is hurting your own hearing. The modern telephone handset and phone systems do not have the capability to send or produce a sound DB level enough to hurt or damage someones hearing. While it might be annoying to the caller, it doesn't harm them, and most likely it "clips" the speaker in their headset so they don't actually hear it.
You guys are the best! Every time I receive a call I don't recognize, I come here. Just about every time it is some bogus call with some leech to society trying to rip all of us off! I read all the reviews and block the freakin' numbers! Saves me a lot of time and heartache!