Make them think they got the wrongest wrong number they've ever called in their life. The caller hears a recorded voice:
"This is the North American Strategic Nuclear Missile Command launch center. Missile launch code received. Thank you Mr President. Have a nice day."
Then for good measure play that scary "end of the world" alarm sound they play at the start of the emergency broadcast system test.-- doctorremulac3, Apr 11 2012 This thing http://www.youtube....watch?v=HgAkxVxo9MU [doctorremulac3, Apr 11 2012] I would think that Emergency Broadcast sound played real loud should do it!-- xandram, Apr 11 2012 If you want to discourage sales calls, it's the auto- dial software you need to frighten, or the management of the call center, not the poor sod making the calls. Unless it's a recording -- clearly, in that case, this idea makes perfect sense.
Playing the fax noise might work better -- it's at least plausible that automated systems would recognize it, and autodialers have an incentive to delete fax numbers from their databases.-- mouseposture, Apr 11 2012 I don't think that this idea will discourage any salespeople at all. Quite the opposite: "Well, since nuclear apocalypse is nigh anyway, how about exchanging some of your soon-to-be- totally-worthless money for something of tangible value, like a magazine subscription? Assuming you survive the initial blast, basic goods like toilet paper are expected to be in very short supply, and you might well be able to trade a copy of Time to a roving gang of bikers in exchange for them not raping and murdering your family in front of you. We'll even throw in a free pint of clean water if you act now!"-- ytk, Apr 11 2012 random, halfbakery