As Open Mike noted, when dual tone tone dialing first came into use, some users,especially people who had been blind from birth, and others with inate good pitch, found that they could whistle the tones needed to dial a call.

One hacker discovered that a plastic whistle packed into boxes of Captain Crunch, an American Breakfast cereal, gave off the two tones needed to access toll-free diaing. This hacker known as Captain Crunch, for the obvious reason had a ball hacking free long distant calls for himself and friends. The originators or Apple Computers, Steve Jobs and Steve Wozniak got some of their start up funds from building and selling Blue Boxes , small electronic boxes that would play the tones needed to take complete control of your phone line, and make these toll free calls. Captain Crunch went to jail for his fun and games, the Steves went on to more honest pursuits.

Dave