From a Bell System booklet titled "The Magic of Communications", dated May
"The first coaxial cable was placed between New York and Philadelphia in
1936 on an experimental basis. The first commercial installation was the
Stevens Point-Minneapolis cable in 1940.
Coaxial cable is now used in a nationwide network of four interconnected
backbone routes: an Atlantic seaboard route from New York to Miami; a
southern transcontinental route from Jacksonville to San Francisco via
Atlanta, Dallas, and Los Angeles; a mid-western route from Philadelphia to
Chicago, via Pittsburgh and Cleveland; and a north-south route from Chicago
to Jackson, Miss., via St. Louis and Memphis."