GSM Shield with Arduino

hello there. how to make arduino + gsm reply the sms to sender automatically? this is the code. please help, thanks.

int timesTosend = 1;
int count = 0;
char phone_no = "";

void setup()
{
// put your setup code here, to run once:
Serial.begin(9600);
delay(2000);
Serial.println("AT+CMGF=1");
delay(200);

}

void loop()
{
checkSMS();
return;
sendSMS();
return;
}

void checkSMS(){
Serial.begin(9600);
Serial.write("AT+CMGF=1\r"); //set GSM to text mode
delay(1500);
Serial.write("AT+CPMS="SM"\r"); //Preferred SMS Message Storage
delay(1000);
Serial.write("AT+CMGR=2\r"); //list the first message from SIM Memory
while(1)
{
if(Serial.available())
{
Serial.write(Serial.read());
}

}
}

void sendSMS(){
delay (1500);
Serial.print("AT+CMGS = "");
Serial.print(phone_no);
Serial.println(""");
while (Serial.read() != '>');
{
Serial.print("from Arduino");
delay (500);
Serial.write(0x1A);
Serial.write(0x0D);
Serial.write(0x0A);

delay (5000);
}
count ++;
}