The first transcontinental telephone call in the United States took place in 1915, and required five operators and 23 minutes to set up the call, from San Francisco to New York.
For many years, long-distance calls required an operator at the calling end and another at the receiving end, and there were often more operators needed at intermediate points to build the route through the network, one segment at a time.
In 1943, AT&T installed the first automatic toll switch, a number 4 crossbar, in Philadelphia, enabling one operator to complete a long-distance call. But the operator might still dial up to 12 digits of routing codes to build the route to the destination, then dial the local phone number, another four to seven digits.
In 1951, AT&T initiated direct-dialed long-distance service. (info from AT&T, photo from Northern Illinois University Libraries )