I had a hipster friend who walked around with a suitcase phone from the early 80's that he had connected with the ancient cellular service that still exists (probably to keep Saudi sheikhs in the deep desert in business or something). It did, in fact, impress.

I used to know a guy who walked around with a rotary handset hooked up to his cell phone back around 04 or 05, it mildly amused more than impressed.

Then a guy farther down the bar sent them a telegram.

Then another guy set off smoke signal warning "C.L.A.P"

Shortly after that, a man in the parking lot laid siege to Carthage and sent them a scroll on foot by dispatching his swiftest Persian boy.

Then a cro-magnon slapped a hand print on the building across the street.

Then a mammoth impaled the original cel phone guy while he tried to mount it for a ride. It's the circlllllle of liiiiife.

Something about rubbing his scent glands against the wall to mark his territory

Trilobite with a telepathy chip installed?

They work with any cell phone. I almost bought one because old handsets are much more comfortable to use than cell phones, but changed my mind when I realized how it would make me look.