We have a 1940s General Post office British black bakelite telephone with a rotary dial in our Technology through Time Collection.
The rotary dial became common in the 1930s and meant that customers could dial directly rather than rely on an operator to do this for them. After World War II, the telephone networks expanded rapidly and more efficient telephone sets, such as the model 500 in the United States, were developed that allowed larger local networks centered around central offices.