Early Hackers Used Whistles From Cap’n Crunch Cereal Boxes

 https://www.atlasobscura.com/articles/capn-crunch-whistle

https://www.popularmechanics.com/technology/a20762221/an-early-hacker-used-a-cereal-box-whistle-to-take-over-phone-lines/

https://telephone-museum.org/telephone-collections/capn-crunch-bosun-whistle/

https://www.computerworld.com/article/2470109/interview-with-iconic-hacker-captain-crunch.html

https://en.wikipedia.org/wiki/Telephone_jack_and_plug

https://en.wikipedia.org/wiki/Don%27t_Call_Us,_We%27ll_Call_You , https://www.youtube.com/watch?v=i4njPe2_rho