Pay telephones appeared as early as 1889. William Gray patented this version, in which a coin dropped into a slot mechanically unlocks the hand crank. While he’s using the phone, the caller keeps the device unlocked by resting his arm on an armrest: “In case the first call is not answered from the central office the user of the telephone can, while keeping his arm upon the arm-rest and so holding the button uncovered, hang up the telephone m on the hook m’ and again call the central office by turning the crank b and pushing in the button in the usual manner.”