Sending command to GSM Modem using php

I have a project on integrating sms module into Joomla interface. I found a php_serial class that enables sending command through serial port by using php. I have tested it through hyperterminal and it works perfectly well, but when I tested it with GSM Modem, the AT command seems to be not working. Anyone has an idea of how to use the php_serial to send AT command to GSM Modem? If you have any clue on how to send AT command using php_serial, please inform me :) Thanks
Here's my code

include "php_serial.class.php";

// Let's start the class
$serial = new phpSerial;

$serial->deviceSet("COM1");
$serial->confBaudRate(115200);
$serial->confCharacterLength(8);
$serial->confParity("none");
$serial->confStopBits(1);
$serial->confFlowControl("xonxoff");

$serial->deviceOpen();

$serial->sendMessage("at+cmgs=\"+6583569765\"\r");
$serial->sendMessage("hello".chr(26));

$serial->deviceClose();

?>