使用CURL和PHP的XML响应POST请求

I have to invoke a soap web service using curl and php. I tried this code:

$ch = curl_init();

$ch = curl_init($url);
            curl_setopt($ch, CURLOPT_MUTE, 1);
            curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
            curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
            curl_setopt($ch, CURLOPT_POST, 1);
            curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: text/xml'));
            curl_setopt($ch, CURLOPT_POSTFIELDS, "<?xml version=\"1.0\" encoding=\"UTF-8\"?><soapenv2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd................</soapenv:Envelope>");
            curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);

$result = curl_exec($ch);

This code works well but I can't to print the result as XML.

If I use other client to invoke the same service I obtain a XML response (this is correct). Why?