An engineer at Motorola made the first known phone call in public from a cell phone on this day in 1973. AT&T, its main competitor at the time, was working on its own system to connect phones using cellular signals. Motorola knew it had to compete, and in fact had its own car phones on the market; but engineer Martin Cooper thought he could do a better job than ol' "Ma Bell," which was planning to use the cell signals for car phones. To Cooper, a car phone may have been "mobile," but it sure wasn't a mobile phone.
So, he and his team put together the DynaTAC, a big brick of a device that weighed over two pounds. Still, it wasn't lugged around in a suitcase or embedded in a car: you could pick it up, make a call, and then put it back down without the hassle.
Development took just 90 days. Cooper, in a demonstration for the press, made the call from the DynaTAC while walking down the street. It was a victory lap for Motorola, not least because Cooper made that call to the director of AT&T's cellular phone program, to rub the breakthrough in the poor guy's face. The AT&T director, as of the 50th anniversary of the call in 2023, claimed not to remember it.
You can learn more about the DynaTAC's development in this article from Gizmodo.