Thanks for Listening (1937)

Homer Tompkins, a trusting young musician with aspirations of becoming a radio star, is installed in a fine set of offices in Reno by a quartet of "easy money" con artists who have bugged rooms and suites, with the title of "professional listener", and he passes off what he hears to his employers--Lulu, Trixie, Maurice, and Champ--and they use the information for blackmail purposes. They also so involve his sweetheart, Toots, that he cannot withdraw even when he finally learns he is being used as a tool.