Lima (Ohio) Daily News, February 24, 1920, page 4:

IF  YOU  EVER  GO  TO  IOWA  BE  SURE  TO  "LISTEN  IN"
    DAVENPORT, Iowa--If your baby cries, let it cry--it won't bother this soloist. And it won't interfere with your hearing grand opera selections, classical and ragtime music, either--if you live near Davenport and "attend" Robert Karlowa's concerts by wireless telephone.
    Nearly every wireless "fan" within a radius of 100 miles of Davenport are enjoying Karlowa's baritone solos every night--and yet they don't have to leave their easy chairs.
    Karlowa calls his "audience" together by calling the various stations on the wireless circuit. As soon as the apparatus is adjusted to the ears the concert begins. With perfect transmission conditions, the entertainment usually lasts an hour.