Regular voice broadcasts didn't begin until the 1920's, after the end of WWI. The first commercial stations began broadcasting in the US in 1920, and the BBC was formed in 1922. Commercial off-the-shelf receivers began to be available about the same time, and radio as a communications medium expanded rapidly.

Not strictly propaganda-related, but Radio Belgrade played something of a prominent role in WWII. The powerful shortwave (684 kHz) transmitter could reach much of Europe and North Africa. After the capture of Yugoslavia by the Germans, they turned the radio station into Soldatensender Belgrad (Soldiers' Radio Belgrade) on August 18, 1941. A lieutenant named Karl-Heinz Reintgen took over the station with a handful of records. One of these was Lale Andersen's song "Lili Marleen". The song of a soldier's love became an instant hit with the German troops and eventually was the last song played by Radio Belgrade every night at sign-off (at 2200 hours). Allied troops in North Africa were also very fond of it, despite not quite understanding the lyrics. It was the subject of one of Bill Mauldin's cartoons, as well.