These early mobile telephone systems can be distinguished from earlier closed radiotelephone systems in that they were available as a commercial service that was part of the public switched telephone network, with their own telephone numbers, rather than part of a closed network such as a police radio or taxi dispatch system.
These mobile telephones were usually mounted in cars or trucks, though briefcase models were also made. Typically, the transceiver (transmitter-receiver) was mounted in the vehicle trunk and attached to the "head" (dial, display, and handset) mounted near the driver seat.
They were sold through WCCs (Wireline Common Carriers, AKA telephone companies), RCCs (Radio Common Carriers), and two-way radio dealers. The primary users were loggers, construction foremen, realtors, and celebrities.
Early examples for this technology:
Parallel to IMTS in the US until the rollout of cellular AMPS systems, a competing mobile telephone technology was called Radio Common Carrier or RCC. The service was provided from the 1960s until the 1980s when cellular AMPS systems made RCC equipment obsolete. These systems operated in a regulated environment in competition with the Bell System's MTS and IMTS. RCCs handled telephone calls and were operated by private companies and individuals. Some systems were designed to allow customers of adjacent RCCs to use their facilities but the universe of RCCs did not comply with any single interoperable technical standard, (a capability called roaming in modern systems). If you had RCC service in Omaha, your phone would not be likely to work in Phoenix. At the end of RCCs existence, industry associations were working on a technical standard that would potentially have allowed roaming, and some mobile users had multiple decoders to enable operation with more than one of the common signaling formats (600/1500, 2805, and Reach). Manual operation was often a fallback for RCC roamers.
Roaming was not encouraged, in part, because there was no centralized industry billing database for RCCs. Signaling formats were not standardized. For example, some systems used two-tone sequential paging to alert a mobile or hand-held that a wired phone was trying to call them. Other systems used DTMF. Some used a system called Secode 2805 which transmitted an interrupted 2805 Hz tone, (in a manner similar to IMTS signaling,) to alert mobiles of an offered call. Some radio equipment used with RCC systems was half-duplex, push-to-talk equipment such as Motorola hand-helds or RCA 700-series conventional two-way radios. Other vehicular equipment had telephone handsets, rotary or pushbutton dials, and operated full duplex like a conventional wired telephone. A few users had full-duplex briefcase telephones, (radically advanced for their day).
RCCs used paired UHF 454/459 MHz and VHF 152/158 MHz frequencies near those used by IMTS.
Using the same channel frequencies as IMTS, the US Federal Communications Commission authorized another 0G technology called Rural Radiotelephone Radio Service. Because RF channels were shared with IMTS, the service was licensed only in areas that were remote from large Bureau of the Census Metropolitan Statistical Areas (MSAs).
Systems used UHF 454 MHz or 152 MHz radio channels to provide telephone service to extremely rural places where it would be too costly to extend cable plant. One such system was on a 454/459 MHz channel pair between the Death Valley telephone exchange and Stovepipe Wells, California. This specific system carried manual calls to the Traffic Service Position System (TSPS) center in Los Angeles. Stovepipe Wells callers went off-hook and were queried, "Number please," by a TSPS operator, who dialed the call. Dial service was introduced to Stovepipe Wells in the mid-1980s. The radio link has since been replaced by cable.