THIS INFO – (pasted here verbatim, .. the links in each paragraph open the source website)
The Carterfone is a device invented by Thomas Carter. It manually connects a two-way mobile radio system to the public switched telephone network (PSTN), making it a direct predecessor to today’s autopatch.
It’s a fascinating case that carries huge implications for today. For decades, AT&T had prohibited consumers from attaching anything but its own phones to its network. In 1968, AT&T tried to bar the use of a “Carterfone”, which linked a mobile radio to a telephone.
Prior to 1968, AT&T maintained a monopoly on what devices could be electrically connected to their phone lines. This led to a market for 103A-compatible modems that were mechanically connected to the phone, through the handset, known as acoustically coupled modems. Particularly common models from the 1970s were the Novation CAT (shown in the image) and the Anderson-Jacobson, spun-off from an in-house project at the LLNL.
In 1968 the U.S. Supreme Court broke AT&T’s monopoly on the lines in the landmark Carterfone decision. Now the lines were open to anyone, as long as they passed a stringent set of AT&T designed tests. Of course AT&T made these tests complex and expensive, so acoustically coupled modems remained common into the early 1980s.
The device was acoustically, but not electrically, connected to the public switched telephone network. It was electrically connected to the base station of the mobile radio system, and got its power from the base station. All electrical parts were encased in bakelite, an early plastic. When someone on the CB radio wished to speak to someone on phone, or “landline” (eg, “Central dispatch, patch me through to McGarrett”), the station operator at the base would dial the telephone number. When callers on the radio and on the telephone are both in contact with the base station operator, the handset of the operator’s telephone is placed on a cradle in the Carterfone device. A voice-operated switch in the Carterfone automatically switches on the radio transmitter when the telephone caller is speaking; when he stops speaking, the radio returns to a receiving condition. A separate speaker is attached to the Carterfone to allow the base station operator to monitor the conversation, adjust the voice volume, and hang up his telephone when the conversation has ended.