Here is a phone designed for hackers and makers in mind. The WiPhone uses WiFi to let you make calls. It features a 2.4″ screen, WiFi, 700mAh battery, and 25 buttons. You can access the 20-pin programmable header on the back of your phone. It supports MicroPython.
You can disassemble the phone with a few screws to modify it for your projects. It is ready for Arduino programming.