flex与php页面传值的问题，在线等

flex中的mxml文件
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<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="vertical">
    <mx:HTTPService url="conn.php"
        id="service"
        result="serviceResult(event)" fault="serviceFault(event)"
        method="post" contentType="application/xml"
        useProxy="false">
        <mx:request xmlns="">
            <id>{requestedId}</id>
        </mx:request>
    </mx:HTTPService>
    <mx:Script>
        <![CDATA[
            import mx.rpc.events.FaultEvent;
            import mx.rpc.events.ResultEvent;
            import mx.controls.Alert;
            
            [Bindable]
            private var requestedId:String;
            
            //trace the result of the service out
            private function serviceResult(event:Event):void {
                trace(service.lastResult.name);
            }
            // in the event that the service faults or times out
            private function serviceFault(event:Event):void {
                trace('broken service');
            }
            private function callService():void {
                try{
                    requestedId = input.text;
                    service.send();
                }catch(e:Error){
                    Alert.show(e.message);
                }
            }
        ]]>
    </mx:Script>
    <mx:TextInput id="input"/>
    <mx:Button label="get user name" click="callService()"/>
    <mx:Text text="{service.lastResult.id}"/>
    <mx:Text text="{service.lastResult.name}"/>
    <mx:Text text="{service.lastResult.age}"/>
</mx:Application>
--------
conn.php<?php
    $id = $_REQUEST['id'];
    echo('<id>'.$id.'</id><name>ok</name><age>30</age>');
?>
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际运行后，flex的确可以访问到index.php，但问题是只能取到 
 echo('<id>'.$id.'</id><name>ok</name><age>30</age>')中的name与age的值，由flex传过去的id为null。
大家帮我想下并解决下，thanks