In February 1876 Alexander Graham Bell invented the telephone in Boston and applied for the patent. Patent no. 174,465, Improvement in Telegraphy, was issued to Bell on March 7, 1876, by the U.S. Patent Office. Bell's patent covered "the method of, and apparatus for, transmitting vocal or other sounds telegraphically . . . by causing electrical undulations, similar in form to the vibrations of the air accompanying the said vocal or other sound." In his invention of the telephone Bell was preceded by Philip Reis, who perfected his device in 1861, and numerous other inventors played lesser or greater roles. However, Bell was the first to create a telephone that could reproduce intelligible speech at the receiving end, and was also the first to patent the telephone. Because of the numerous other inventors involved there was unusually extensive and historic litigation over the telephone patents, culminating in Bell's victory. Among the controversies was the question of the priority of Elisha Gray in the invention.
As the well-known story goes, on March 10, 1876 Bell spoke the first words through the instrument to his assistant, Thomas A. Watson, in the next room. Bell said, "Mr. Watson— come here— I want to see you." This was Bell's first proof that his invention actually worked.
Bell presented his first report on the telephone to the American Academy of Arts and Sciences in Boston on May 10, 1876. His report, "Researches in telephony," was published in Proceedings of the American Academy of Arts and Sciences, new series 4 (whole series 12) (1877) 1-10. Bell's telephone did not become commercially viable until 1878.
♦In December 2013 a digital facsimile of Bell's laboratory notebook recording his March 10, 1876 experiment was available from the Library of Congress at this link.
Hook & Norman, The Haskell F. Norman Library of Science & Medicine (1991) no. 164.