In 1956, TAT-1, the first submarine transatlantic telephone cable system, was inaugurated.
Before TAT-1, voice was carried across the Atlantic on unreliable and expensive radio channels. TAT-1 operated until 1978.
Learn more at http://www.ieeeghn.org/wiki/index.php/Milestones:The_First_Submarine_Transatlantic_Telephone_Cable_System_(TAT-1),_1956.