Teresi out and ultimately meeting him at his home in the San Jose suburbs. Teresi told Draper about a network of friends who called themselves phone phreaks, many of whom were also blind. Using cassette tape recordings and a Farfisa electric organ to replicate electronic tones used to control it, they explored the phone network to understand how it worked and to make free long distance calls. Among the group of friends was Joseph Engressia, who went by the moniker Joybubbles, who had perfect pitch and could whistle precisely the 2600 hertz tone used by AT&T to indicate that a trunk line was available to make a call. Gathering around clusters of payphones, they would play the tones into the receiver and explore the network, calling distant locations for free.

Draper learned from Teresi that a toy whistle packaged in boxes of Cap'n Crunch cereal in 1963 emitted the same 2600-hertz tone precisely. The tone disconnected one end of the trunk while the still-connected side entered operator mode. The vulnerability they had exploited was limited to call-routing switches that relied on in-band signaling.

Learning of Draper's knowledge of electronic design, Teresi and other phreakers asked him to build a multifrequency tone generator, known informally as a blue box, that could play the 2600-hertz tone and other tones associated with controlling the phone network. Draper built his first crude electronic blue box and soon designed a more sophisticated one. By 1970, the phreaking hobby had spread, and its enthusiasts in the know had started to gather regularly on a conference call-like system they called 2111. The name came from a misconfigured teletype switching machine in British Columbia designed for connecting multiple teletype lines at once. The phreakers discovered that if they called the number at the same time, they would all be connected at once, creating a primitive conference call. During one of these calls, Draper took on the moniker Captain Crunch, inspired by the toy whistle.