Radio

The radio was the first device that made mass communication possible. It was one of the first devices to be able to communicate internationally. In the 1860's, a Scottish Physicist named James Maxwell discovered radio waves, electromagnetic waves that have the capacity to transmit music and speeches. The first development of the radio began in 1893 when Nikolai Tesla demonstrated wireless radio communication in St. Louis, Missouri. In 1896, Guglielmo Marconi was awarded with the official patent of the radio by the British Government. 
Without the telegraph and the telephone the radio would be nothing. Radio-telegraphy is sending radio waves that contain morse code that is used in a telegraph. The first use of radio transmitters was used for ship-to-shore and ship-to-ship communication. When a ship was sinking it would use the radio to reach nearby stations to call for aid.
In 1912 The Radio Act required all land radio stations and ship stations to be staffed  24 hours a day, 7 days a week. In the late 80's and 90's the radio started expanding with radio stations that broadcasted sports and comedy acts.

Sources - 

http://www.personal.psu.edu/jtk187/art2/radio.htm

http://inventors.about.com/od/rstartinventions/a/radio.htm