A few years after showing my mom how to beat the phone company out of long distance charges a kid in California figured out that when he blew his Captain Crunch whistle (meaning, a free plastic whistle inside a box of Captain Crunch) into a telephone receiver he was able to make phone calls from any pay phone for free. Not only local calls, but long distance calls as well. Back then long distance calls were expensive, especially overseas calls. The plastic Captain Crunch whistle hit a perfect frequency of 2600 hertz, a frequency that caused the phone company's equipment to open a channel that allowed for unrestricted calls throughout their system. So a kid in San Jose could call his grandma in Topeka for free, which sounds relativity harmless, but salesman in New York City could use the same whistle to call his customer in Tokyo. A free plastic whistle cost the phone company millions of dollars in lost revenue, but many more millions in research and development to defeat the problem. Ma Bell's entire network of switching equipment had to be redesigned and replaced to stop access a free plastic whistle. It was such a massive undertaking for the phone company to correct this problem that the Captain Crunch hack still worked years after the phone company learned of it.
Perhaps more significant, the Captain Crunch hack introduced American kids to the concept of a hack. Once theses kids started thinking in this direction there was no stopping them. The phone was merely the first to be hacked. When personal computers were introduced phone hackers found a new toy, a new challenge. Hacking as we know it began in the late 70's with the Apple Computer, but hacking actually began with The Captain Crunch Whistle. It was so significant to hacking's foundation that in 2001, the last year I had access to the internet, the premiere hacker resource site was named in it's honor, Alt2600.com (I believe the website is now called 2600.com).
I would become a decent hacker myself, and like most others, my first hacks were phone hacks. Over the years there have been numerous ways to hack the phone, but eventually the phone company would figure out how to prevent them all. Yet no matter how advance the phone company's security, there is always the low tech method that I figured out when I was six. The last time I did a phone hack was while fugitive in 2001 and I used the same method I had suggested to my mom in 1962.
Read more about Clayton telling his mom how to beat the phone company charges, in his biography, here.