The radio transmitters used for the Catalina Island, California telephone link could be readily picked up by most standard radio receivers, which allowed eavesdropping on the conversations. There were also reports that at night the telephone conversations were being heard at least as far away as Colorado. And the problem worsened with the broadcasting boom of 1922, when large numbers of the public bought radios. The telephone company eventually began to scramble the transmissions, and later replaced this first radiotelephone link with an undersea cable.
Pacific Radio News, October, 1920, pages 58, 60:


    "Tuning in" on some of the wireless telephone communications floating about southern California's sunny atmosphere is becoming quite a sport. All of which, it might be added, is illustrative of the fact that wireless telephone communication is far from a private means of intercourse.
    Recently this new and modern system has been installed at Catalina Island. Switch board operators at San Pedro and on the island are able to connect up parties with the main land telephone system and points on the resort island via wireless. In fact it is now possible to communicate from Redlands via long distance and wireless to a friend, sweetheart, mother-in-law or otherwise, who perchance may be stopping at the St. Catherines Hotel. It is beyond the experimental stage and is proving quite popular and commercially satisfactory.
    However, don't get the idea that one can't listen in on a wireless message. That's where the "tuning in" comes in. It's a part of the mechanical equipment which permits anyone familiar with the game to pick up messages passing through the air within range of his receiving apparatus. It also is possible for a third party to "butt into" the conversation.
    As an illustration. Yesterday afternoon, a young lady, at least her voice was that of a young lady, called the room clerk at the St. Catherines Hotel from Los Angeles. She requested that a room with twin beds be reserved for her over the week end. And just then, some big gruff voiced gob, presumably on one of Uncle Sam's destroyers, somewhere in the Pacific, broke in and inquired what caused the argument. The room clerk is trying yet to square himself with the prospective customer.
    Then another example. Late last evening another conversation was overheard. A young lady in Pasadena was conversing with her fiance at Catalina. "Did you get my last letter?" she asked. "Yes," he replied. "Well, John, don't pay any attention to what I said in that letter because I didn't mean a word of it and I'm sorry," she said. And John said that was all right as he was used to getting such letters--and bang again, went the second receiver and all communication was lost.
    Shortly afterward a staff member of a Los Angeles afternoon newspaper was heard to relay via wireless baseball scores from the eastern leagues. And immediately following he dispatched a few late stock market quotations. Yes--after all--it's a fascinating game. But take warning. There are any number of amateur wireless telephone operators in the community who can steal your message. It's done by "tuning in," a mechanical process which is highly entertaining.