ผมเขียนแบบนี้ครับ
#include "SIM900.h"
#include <SoftwareSerial.h>
#include "inetGSM.h"

InetGSM inet;

/*char msg[50];
int numdata;
char inSerial[50];
int i=0;*/
boolean started=false;

void setup()
{
  //Serial connection.
  Serial.begin(9600);
  Serial.println("GSM Shield testing.");

  if (gsm.begin(2400)){
    Serial.println("\nstatus=READY");
    started=true;  
  }
  else Serial.println("\nstatus=IDLE");

  if(started){

    if (inet.attachGPRS("internet.wind", "", ""))
      Serial.println("status=ATTACHED");
    else Serial.println("status=ERROR");
    delay(1000);

    gsm.SimpleWriteln("AT+CREG=1");
    delay(5000);
    gsm.WhileSimpleRead();
    gsm.SimpleWriteln("AT+CGATT=1");
    delay(5000);
    gsm.WhileSimpleRead();
    gsm.SimpleWriteln("AT+CGDCONT=1,\"IP\",\"internet\"");
    delay(5000);
    gsm.WhileSimpleRead();

    gsm.SimpleWriteln("AT+CIFSR");
    delay(5000);
    gsm.WhileSimpleRead();

    gsm.SimpleWriteln("AT+CIPHEAD=1");
    delay(5000);
    gsm.WhileSimpleRead();

    gsm.SimpleWriteln("AT+CIPSTART=\"TCP\",\" www.pongtongt.freetzi.com\",\"80\"");
    delay(5000);
    gsm.WhileSimpleRead();
    gsm.SimpleWriteln("AT+CIPSEND=1");
    delay(1000);
    gsm.SimpleWriteln("GET /test.php?val=123 HTTP/1.1");
    delay(1000);
    gsm.SimpleWriteln("host: www.pongtongt.freetzi.com");
    delay(1000);
    gsm.SimpleWriteln("0x1A");
    delay(3000);
    gsm.WhileSimpleRead();             ///มาถึงตรงนี้มันค้างอยู่ที่ > ซึ่งมันจะต้อง ขึ้นว่า SEND OK แก้ยังไงดีครับ หรือผมเขียนผิดตรงไหน
    

    //Serial.println("host:  http://pongtongt.freetzi.com");  



    //
    //Serial.println("Ctrl+Z");
  }
};

void loop()
{
  //Read for new byte on serial hardware,
  //and write them on NewSoftSerial.
  // serialhwread();
  //Read for new byte on NewSoftSerial.
  // serialswread();
};