RePhone Lets You Turn Anything Into A Phone | TechCrunch
The project is actually a tiny circuit board with a SIM slot and an optional screen. It also supports Bluetooth. You’re going to want to get the $49 Kit Create, a tiny watch-like system that includes a little case and all the modules. It’s like getting a tiny unlocked cellphone for under $50. This is obviously an experimental board but I checked it out a week ago and it seemed to work fairly well. It includes programming libraries in Arduino IDE, Lua and Javascript that allow you to connect the phone to the web and even IFTTT…

Finally, game cartridges you can plug in to your smart phone: Pico Cassette sends data through the headphone jack using audio signals | ARS Technica
Enter Pico Cassette, a Japanese outfit that says it’s bringing back “the next retro” with tiny game cartridges that plug in to a smartphone’s headphone jack. The tiny “cassettes” (the general Japanese term for cartridges) are built on PlugAir technology, which uses a specially designed iPhone or Android app to draw power from the headphone jack and send data using specially modulated audio signals…