介绍如何使用sim900a发送接收中文和英文短信，如何拨打电话及接听，挂断电话，如何使用gprs。-Describes how to use sim900a to send and receive Chinese and English message, how to call and answer, hang up the phone, how to use the gprs.

主要讲解如何使用SIM-900A模块与STM32单片机进行短信收发和电话接收(Mainly explain how to use SIM-900A module and STM32 microcontroller for SMS transceiver and telephone reception)