Here is the breakdown of what you are downloading and how to use it.
// Send an SMS message void send_sms(char *number, char *message) gsm_send_atcommand("AT+CMGF=1\r"); gsm_send_atcommand("AT+CMGS=\""); gsm_send_atcommand(number); gsm_send_atcommand("\"\r"); gsm_send_atcommand(message); gsm_send_atcommand("\r"); gsm sim900a library for proteus download
Proteus_GSM_SIM900A_Library_v2.0.zip Contents: Here is the breakdown of what you are