Push button telephone.

An experimental model of a push button telephone being developed at Bell Telephone Laboratories is shown as it would be used. The pushbutton telephone is made feasible today by electronic advances which include the transistor, invented at Bell Laboratories. This particular pushbutton design combines many features that promote the greatest accuracy and that are most preferred by users. The pushbutton arrangement is the result of months of human-factors study. (Photo by: Universal History Archive/Universal Images Group via Getty Images)