A maker who calls himself Mr. Volt created a retro designed working prototype of a rotary cell phone. The Arduino based phone has six functions including making calls, storing one phone number, sending a message to that phone number, an FM radio, sleep mode, and system settings.
The body was 3D printed, and Volt posted the full design file to Autodesk so other makers can create their own.
A friend gave me a rotary phone mechanism years ago, and I finally got around to turning it into a working cell phone! It can call, text, play FM radio, and store one whole phone number.