My flash code:

var request=new URLRequest('http://localhost/test.php');
request.method = URLRequestMethod.POST;
var data = new URLVariables();
var bytes:ByteArray = new ByteArray();
bytes.objectEncoding = ObjectEncoding.AMF3;
//write an object into the bytearray
bytes.writeObject( 
      { myString:"Hello World"} 
);
data.data = bytes;
request.data = data;

var urlLoader:URLLoader = new URLLoader();
urlLoader.dataFormat = URLLoaderDataFormat.BINARY;
urlLoader.addEventListener(Event.COMPLETE, onCompleteHandler);
urlLoader.load(request);

function onCompleteHandler(evt:Event):void {
 trace(evt.target.data);
}

PHP code:

define("AMF_AMF3",1); 
$data = $_POST['data'];
echo amf_decode($data, AMF_AMF3);

Basically I need to send an AMF3 object from Flash to PHP and unserialize it. I'm using AMFEXT extension but couldn't get it to work. Any idea?