I went to an IET talk on the history of mobile phone development. It was mostly from an RF perspective. The thing that intrigued me most is that he mentioned the ZX Spectrums. He reminded us that they were usually programmed by cassette tape. All those bleeps and bips were digital 0s and 1s being read in. You get a similar effect if you phone a fax machine by mistake. No wonder they took so long to load a game if you could actually hear the 0s and 1s going into the computer.