This is the Arduino based rotary mobile phone built by Redditor Mr_Volt. It has a small OLED display, is capable of making rotary phone calls, and has enough memory to store a single number. Wow! It also has a sleep mode and — AND — an FM radio. Your grandpa is so jealous right now. Well, I mean he would be if he were awake to see this and not snoring in his La-Z-Boy. Let’s hide his teeth so he calls us whippersnappers!

Keep going for a video of the phone in use.

Source: Geekologie – Man Builds Prototype For A Rotary Cellphone