PHP accessing AT command

<?php
//error_reporting(-1);
require "php_serial.class.php";
// Source: https://github.com/Xowap/PHP-Serial/blob/develop/src/PhpSerial.php
$serial = new phpSerial;
$serial->deviceSet("COM4");
$serial->confBaudRate(9600);                    // Baud rate: 9600
$serial->confParity("none");                    // Parity (this is the "N" in "8-N-1")
$serial->confCharacterLength(8);                // Character length     (this is the "8" in "8-N-1")
$serial->confStopBits(1);                   // Stop bits (this is the "1" in "8-N-1")
$serial->confFlowControl("none");               //
$serial->deviceOpen();                      // Then we need to open it
$serial->sendMessage("AT+CUSD=1,'*152#',15");           // To write into
sleep(3);                           // wait for modem to send message
$read=$serial->readPort();                  // read the response
$response = $serial->_dHandle;

echo "Response: ".$response."<br>";

//echo get_resource_type ( $serial->_dHandle );exit;

if(is_resource($serial->_dHandle) AND !feof($serial->_dHandle))
{
    print_r(stream_get_meta_data($serial->_dHandle));

    $stdin = fopen('php://stdin', 'r');
    $res = stream_get_contents($stdin, -1, 10);

    //var_dump(fread($stdin,8));
    var_dump($res);
    //print_r(stream_get_meta_data($stdin));
}else{
    echo "no response";
}
$serial->deviceClose();
?>