For this first, ceremonial call, Bell (center) was in New York City.
Pictured from left to right: John J. Carty, chief engineer of AT&T; George McAneny, president of the New York City board of aldermen; U.N. Bethell, vice president of AT&T; Alexander Graham Bell; John Purroy Mitchel, mayor of New York City; C.E. Yost, president of Nebraska Telephone Co.; and William A. Prendergast, comptroller of NYC.
The completion of the line in advance of the 1915 World's Fair was a great engineering accomplishment. Devised under the umbrella of Bell System parent American Telephone and Telegraph (AT&T), the line was largely built by local telephone companies. The stretch from Denver to San Francisco was especially difficult as the lines crossed the Rocky Mountains and vast undeveloped stretches of Nevada desert.
Anthea Harris, executive director and CEO of the California Historical Society, left, assists AT&T's McNeely as he demonstrates use of one of the historic phones while taking a selfie with a more modern phone, the iPhone 6.
AT&T needed to work on the amplification of electrical signals, and eventually, with the help of inventor Lee de Forest, developed vacuum tube amplifiers -- a key innovation in extending the New York-Denver circuit the rest of the way to San Francisco.
The last pole on the transcontinental telephone line was put in place on June 17, 1914.
The line stretched 390 miles from New York to Pittsburgh, 545 miles to Chicago, 500 miles to Omaha, 585 miles to Denver, 580 miles to Salt Lake City, and 770 miles to San Francisco -- close to 3,400 total miles across the country to make voice possible coast-to-coast for the first time.