SmithsonianMag has a short piece on the history of the pay phone, which went from a massive communication innovation to a physical reminder of a pre-cellular age in hardly any time at all:
Gray’s first prototype device involved a box that covered the mouth of the receiver and would slide away when a coin was deposited. However, it was rejected on the grounds that one coin could buy several phone calls and that if another station was called, the receiver would also have to pay – obviously not an ideal solution. After a few more failed attempts, Gray found the suprisingly simple solution: a “coin-controlled apparatus” that used a small bell to signify the operator when a coin was deposited (US 408,709), and, a couple years later, a more elaborate “signal device for telephone pay stations” (US 454,470).
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