Key West, Florida - Christmas Day marks the anniversary of the first international telephone call, which was made 100 years ago between Key West and Havana.

The call on December 25 1900, was an experiment to determine whether the human voice could be carried over telegraph wires.

John Atkins, then manager of the Key West office of the International Ocean Telegraph Company, adjusted the wires and called Havana.

"For a long time there was no sound, except the roar heard at night sometimes, caused by electric light current," Atkins told the Florida Times Union and Citizen, which reported the historical call in its December 26 1900, editions.

Atkins continued to call Cuba and finally came back the words, clear and distinct: "I don't understand you."

With those words, international voice communication began.

According to the newspaper, the Southern Bell Telephone Company had connected telephone wires with the existing underwater telegraph cable running between Key West and Havana, said Tom Hambright, director of the Florida History Room at Key West's public library.

The test demonstrated that the technology would work, Hambright said. By 1921, the Miami Metropolis reported it had laid three underwater telephone cables between Key West and Cuba's capital that "in a fortnight will make it possible to talk over the telephone from New York to Havana."

The cables, covering approximately 204km across the Florida Straits in waters in some places more than 2km deep, were touted as the longest telephone cables in the world, Hambright said.

The construction was accomplished by the Cuban-American Telephone and Telegraph Company, a subsidiary of AT&T and the International Telephone and Telegraph Company.

By 1930, the original cables were insufficient and a new cable was installed that provided the same number of telephone circuits as the three older lines. - Sapa-AP