February 20

1928: A telephone line between Sweden and the U.S. is officially opening. The first calls between Stockholm and New York had already taken place on November 29, 1927, however. The first ever transatlantic telephone call was made via radio from New York to London on January 7, 1927.

Transatlantic telephone service was at the time radio-based. Putting down an actual telephone cable demanded a number of technological advances, which did not arrive until the 1940s. 

Source: http://www.nordstjernan.com/news/sweden/5206/