Ed Tannenbaum - Tsukuba Expo (1985)

Nobutoshi Kihara - Sony Walkman (1979)

The original blue-and-silver Walkman model TPS-L2 went on sale in Japan on July 1, 1979. In the UK, it came with stereo playback and mini headphone jacks, permitting two people to listen at the same time (though it came with only one pair of MDR-3L2 headphones). Where the Pressman had the recording button, the Walkman had a "hotline" button which activated a small built-in microphone (the Pressman), partially overriding the sound from the cassette, and allowing one user to talk to the other over the music. The dual jacks and "hotline" button were phased out in the follow-up Walkman II model.
LINK: Source & Pocket Calculators Walkman Museum.