a) New York and San Francisco

The first transcontinental telephone call in the U.S. was made in 1915 between New York and San Francisco. This historic call, involving Alexander Graham Bell in New York and his former assistant Thomas Watson in San Francisco, demonstrated the feasibility of long-distance telephone communication. The call was a monumental achievement in telecommunications, symbolizing the dawn of a new era in connectivity and communication. It marked the beginning of the modern telecommunications network, profoundly impacting business, government, and personal communication.