Although it's getting increasingly easy to imagine a nationwide monopoly on phone service, we haven't technically been there since AT&T was broken up in 1984. Before that, it ran a nationwide, regulated monopoly on telephone service. In 1970, the company produced a video defending and explaining that monopoly — the FCC had just approved the Carterfone two years earlier, paving the way for different telephones to attach to the network. In the video, AT&T refers to this "equipment not owned by the telephone company" as a threat: "When your phone doesn't work, you, and a lot of other innocent people are in trouble." AT&T also raised concerns about other long-distance carriers that were competing with the company would eventually raise the cost of phone lines for rural areas.
Of course, that apocalyptic telecommunications failure didn't come to pass, but it's fun to see how AT&T defended it's monopoly. AT&T is probably hoping it's good fun too, as its description on YouTube simply states "Note that this film is presented for historical interest only, and does not reflect in any way current AT&T policy or positions."
Update: AT&T has mysteriously marked the video as private, preventing anyone from watching the video. We've reached out to the company to see why it has been pulled.
Update 2: AT&T has informed us that the video was posted in error and subsequently pulled.