The BRAINS! of the project were originally supposed to be an Arduino Pro 5v/16Mhz. This was not a deeply considered choice, it’s just what I happened to have lying around. When that didn’t have enough memory, I briefly tried using an Arduino Mega, but that too failed to have enough memory for a simple port of the zip interpreter running the Zork I story file. (It wanted to malloc 32KB of sram, and the Mega has only 8KB of sram). A port that took advantage of the large program space and used sram more efficiently might be possible, however, seemed too ambitious in the time alloted.
The next strategy involved using a single-board-computer (SBC) called a FitPC, and having it use the Arduino Pro only to interface with the phone. This was what was ultimately used in GruePhone 1.0
The second incarnation (GruePhone 2.0) is based on a “chip” computer, which retails for $9, though accessories like a battery and video cable increased that significantly.