1858, Ireland to Newfoundland.
1858, Ireland to Newfoundland.
But no real commercial voice links until 1956... from wiki -
When the first transatlantic telegraph cable was laid in 1858 by businessman Cyrus West Field, it operated for only three weeks; subsequent attempts in 1865 and 1866 were more successful. Although a telephone cable was discussed starting in the 1920s, to be practical it needed a number of technological advances which did not arrive until the 1940s. Starting in 1927, transatlantic telephone service was radio-based.
TAT-1 (Transatlantic No. 1) was the first transatlantic telephone cable system. It was laid between Gallanach Bay, near Oban, Scotland and Clarenville, Newfoundland between 1955 and 1956 by the cable ship Monarch. It was inaugurated on September 25, 1956, initially carrying 36 telephone channels.