I haven’t been able to find this again, but there’s a short film that was made in England in 1946 that perfectly nailed how cell phones were going to work. There was even a man in a grocery store calling his wife at home to find out what ingredient he needed to pick up. The only difference was scale: the man was using a walkie-talkie, which despite the movie images of an officer using a device about 1’x4"x4", in fact also required a ginormous and heavy backpack thing lugged around by some misbegotten private.

BTW a fun fact: the word “ginormous” (a portmanteau word combining “gigantic” and “enormous”) dates to WWII or earlier. I’d always assumed it was valley-girl speak until I encountered it in a Battle of Britain memoir written by a pilot who was killed in 1942.