Joybubbles (the legal name of the former Joe Engressia since 1991), a blind genius with perfect pitch who accidentally found he could make free phone calls by whistling tones and went on to play a pivotal role in the 1970s subculture of “phone phreaks,” died on Aug. 8 in Minneapolis. […] Well before the mid-1970s, when digitalization ended the tone-based system, Joybubbles had stopped stealing calls.
Source: wiktionary