File content as of revision 0:c9d0008613d6:

#include "mbed.h"

#define CTRL_Z      26      //Attach at the end of this message string

Serial pc(USBTX, USBRX);
Serial SIM800L(P3_1, P3_0);
DigitalOut led1(LED1);

char phone[14] = "\"17039739276\"";
char buf[40];
char buf1[40];

long GSMBAUD = 9600;
long PCBAUD  = 9600;

int main(){
    pc.baud(PCBAUD);
    SIM800L.baud(GSMBAUD);
    
    //wait(0.1f);
    SIM800L.puts("AT\r\n");
    SIM800L.scanf("%s", buf);
    SIM800L.scanf("%s", buf1);
    pc.printf("%s\n", buf);
    pc.printf("%s\n", buf1);
    
    //wait(0.01f);
    
    SIM800L.puts("AT+CMGF=1\r\n");
    SIM800L.scanf("%s", buf);
    SIM800L.scanf("%s", buf1);
    pc.printf("%s\n", buf);
    pc.printf("%s\n", buf1);
    
    //wait(0.01f);
    SIM800L.puts("AT+CMGS=\"17039739276\"\r\n");
    //SIM800L.puts("\r\n");
    
//    SIM800L.scanf("%s", buf);
//    SIM800L.scanf("%s", buf1);
//    pc.printf("%s\n", buf);
//    pc.printf("%s\n", buf1);
    
    wait(0.1f);
    
    SIM800L.printf("This is the automatted program SMS from SIM800L. :D %c\r\n", CTRL_Z);
    //wait(4);
    //SIM800L.puts("26\r\n");
    
    //wait(0.1f);
    SIM800L.scanf("%s", buf);
    SIM800L.scanf("%s", buf1);
    pc.printf("%s\n", buf);
    pc.printf("%s\n", buf1);
    
    wait(1);
    
    //pc.printf("Yike");
    SIM800L.puts("AT+CMGF=0\r\n");
    SIM800L.scanf("%s", buf);
    SIM800L.scanf("%s", buf1);
    pc.printf("%s\n", buf);
    pc.printf("%s\n", buf1);
}