Starting in 1946, with a pilot program in St. Louis, Missouri, AT&T launched its Mobile Telephone Service (MTS). By 1948 the service was available in 100 cities and towns and along highway corridors. The service ran on 25 VHF radio channels, using half-duplex FM; handsets on mobile installations had a push-to-talk button. All calls were placed through human operators. Here is a Bell System promotional film from the late 1940s about the wonders of mobile telephony and how it worked.
The separate tube-based transmitter and receiver weighed 36 kg together and were usually mounted in the trunk of automobiles, taking up a substantial part of the space. The film notes that the installation “may require a larger battery and generator”. The service was horrifically expensive. In present-day (2020) dollars, the subscriber fee was around US$180 per month, and local calls cost between US$3.60 and US$4.80. The service was never very popular, with no more than 5,000 subscribers placing around 30,000 calls a week. The limited number of VHF channels would have precluded expanding much beyond that, anyway.