Turns out the venerable plug goes back to at least 1878. Keep in mind, I’m talking about the good old fashioned 1/4″ phone jack with two wires. Over time, the jack and plug have spawned ...

See: Headphone Jack (3.5mm) 2.5mm connectors are still common for TTY devices for the hearing impaired. Therefore most modern phones require a 3.5mm-to-2.5mm adaptor in order to connect to a TTY ...