In late 1906, Reginald Fessenden had developed an alternator-transmitter, located at Brant Rock, Massachusetts, to the point that it was a reliable transmitter for audio signals. In December of that year, he began presenting a series of demonstrations of the transmitter's capabilities to interested groups of scientists and business representatives. This was followed by more general tests, culminating, on the evenings of December 24, 1906 (Christmas Eve) and December 31, 1906 (New Year's Eve) in two transmissions which are generally believed to be the first-ever entertainment broadcasts by radio. Unfortunately, there do not seem to be any contemporary accounts of these broadcasts -- the review below was apparently extracted from a letter Fessenden wrote twenty-five years later to S. M. Kinter on January 29, 1932, and appears to be the only existing first-hand account. (James E. O'Neal covers the surprising lack of supporting documentation for Fessenden's claim to have made these broadcasts in Fessenden: World's First Broadcaster?, while John S. Belrose is more convinced, and includes the full text of Fessenden's letter, in Fessenden's 1906 Christmas Eve Broadcast)

Moreover, although the alternator-transmitter's possible use for distributing music and information was noted at the time, Fessenden's subsequent work concentrated almost exclusively on developing it for private point-to-point communication, as an adjunct to the wire telephone system, and these two publicity broadcasts seem to be the sum-total of his broadcasting career.
 

Builder of Tomorrows, Helen Fessenden, 1940, pages 153-154:

CHAPTER  XV

WIRELESS  TELEPHONY  AND  THE  HIGH-FREQUENCY  ALTERNATOR

    On Christmas Eve and New Year's Eve of 1906 the first Broadcasting occurred. Three days in advance Reg had his operators notify the ships of the U.S. Navy and of the United Fruit Co. that were equipped with the Fessenden apparatus that it was the intention of the Brant Rock Station to broadcast speech, music and singing on those two evenings.
    Describing this, Fessenden wrote:--
    "The program on Christmas Eve was as follows: first a short speech by me saying what we were going to do, then some phonograph music.--The music on the phonograph being Handel's 'Largo'. Then came a violin solo by me, being a composition of Gounod called 'O, Holy Night', and ending up with the words 'Adore and be still' of which I sang one verse, in addition to playing on the violin, though the singing of course was not very good. Then came the Bible text, 'Glory to God in the highest and on earth peace to men of good will', and finally we wound up by wishing them a Merry Christmas and then saying that we proposed to broadcast again New Year's Eve.
    The broadcast on New Year's Eve was the same as before, except that the music was changed and I got someone else to sing. I had not picked myself to do the singing, but on Christmas Eve I could not get any of the others to either talk, sing or play and consequently had to do it myself.
    On New Year's Eve one man, I think it was Stein, agreed to sing and did sing, but none of the others either sang or talked.
    We got word of reception of the Christmas Eve program as far down as Norfolk, Va., and on the New Year's Eve program we got word from some places down in the West Indies."
It is not surprising that it was widely heard even beyond the group of Fessenden equipped boats--for as he further states--
    "As a matter of fact, at the time of the broadcast, practically everyone was infringing the liquid barreter. When the broadcast was made, practically every ship along the coast was equipped to receive it."