phreaking

/ˈfrikɪŋ/
noun
  1. The activity of exploring or exploiting telephone systems, often to make free calls or understand how they work.
    • Phreaking became popular in the 1970s when people discovered they could use toy whistles to mimic phone tones.
    • The movie shows a group of teenagers getting into phreaking as a way to call anywhere in the world for free.
    • Modern phreaking is rare because most phone systems are now digital and harder to trick.
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