Sharath N25 has published a great tutorial to the Instructables website providing the full tutorial on how to build your very own basic mobile phone using the STM32F407 Discovery Kit and a GSM A6 Module. The project contains three main modules a LCD 16×02 display for visual output, a flexible Hex keypad for input the already mentioned GSM A6 Module, used for making and receiving calls as well as SMS messaging, all powered by the STM32F407 MCU which controls the components.
“Have you ever wanted to create a cool embedded project?. If yes, how about building one of the most popular and everyone’s favorite gadget i.e Mobile Phone!!!. In this Instructable, I will guide you on how to build a basic mobile phone using the STM32F407 Discovery Kit and GSM A6 module. To make programming simple and organized, I developed individual driver code for Interfacing GSM A6 module, LCD and Keypad on STM32F407 MCU. Then I simply included these driver files in the main program and called respective APIs. You can find these driver codes in the Supplies below.”
For full instructions on how to build your very own basic mobile phone jump over to the project page by following the link below. The GSM A6 Module is powered using a micro USB connector.