The easiest way to design one's own cell phone is through the use of an Arduino microcontroller and a GSM Arduino shield. These two components can be combined with user interface components, such as buttons and screens, to create a basic cell phone capable of making calls and text messages.
The Arduino microprocessor is an open source microcontroller that can be configured to act as the brains of a DIY cell phone. To configure the Arduino properly, it must be attached to a computer via USB and coded in a program called the Arduino Environment. In this program, users must either code their own program using C++ or download pre-existing code from the Internet. Upload the code to the Arduino itself to teach the microcontroller how to process cell signals.
An Arduino GSM shield is also required to design one's own cell phone. This piece of hardware allows the Arduino to interface with a standard SIM card, allowing users to connect to a cellular network.
In addition to the GSM shield and the Arduino, a cell phone must also implement user interface components. The most basic cell phones achieve this with an array of buttons and a screen. These components attach directly to the Arduino and allow users to alter the microcontroller's purpose.