The car phone was invented in 1946. 1973 was nerar the end of their widespread use, as the handheld mobile phone was becoming more usable due to the invention of the first commercial cellphone system and the beginnings of its widespread use.

The carphone was basically a high-powered two way radio hooked up at the tower end to the telephone system. Since it had a powerful transmitter (relative to a cell phone) it could be used much further from a tower than a cell phone. In 1973 you would be able to use one in pretty much every medium-sized and large city and a lot of rural areas as well.