American Telephone and Telegraph Building, ca. 1917.

The 29-story building, also known as 15 Dey Street, was designed by architect William Welles Bosworth as the headquarters of the American Telephone and Telegraph Company. Construction was completed in stages between 1912 and 1916.

In 1915, the building hosted the Atlantic end of the purported first transcontinental telephone conversation (the technology had previously been tested (also from this building); this call was a demonstration for marketing purposes). Alexander Graham Bell reprised his famous call to Thomas Watson, who this time answered from San Francisco.