While it’s hard to beat today’s mobile devices functionality-wise, if you need a phone built like a tank and designed for voice communication and voice communication only, you can’t go wrong with the Western Electric Model 500 rotary telephone. As maker “bicapitate” shows on Imgur, these models include a generous amount of space inside, enough room in fact for an Arduino Uno along with a tiny Adafruit FONA module for cellular capabilities.

While project details are slim, it appears that the Uno takes pulses from the rotary input, then makes calls via the FONA. A DC motor drives the bell to indicate a call is being made, and the original headset, possibly modified with a new speaker and mic, is used for audio. It now also includes a LiPo battery, allowing you to use this wherever convenient—while still slamming the headset down with authority!