<?xml version="1.0" encoding="utf-8"?>
<methodCall>
<methodName>groups.getGroupMembers</methodName>
<params>
 <param>
  <value>
   <struct>
    <member>
     <name>GroupID</name>
     <value>
      <string>12345</string>
     </value>
    </member>
    <member>
     <name>RequestingAgentID</name>
     <value>
      <string>12345</string>
     </value>
    </member>
   </struct>
  </value>
 </param>
</params>
</methodCall>

curl -i -d @myfile.xml -X POST -w '%{http_code}\n'  http://server

$request = xmlrpc_encode_request("groups.getGroupMembers", array(
    "GroupID" => "12345",
    "RequestingAgentID" => "12345"
));
//create the stream context for the request
$context = stream_context_create(array('http' => array(
    'method' => "POST",
    'header' => "Content-Type: text/xml\r\nUser-Agent: PHPRPC/1.0\r\n",
    'content' => $request
)));

//URL of the XMLRPC Server
$server = 'http://server';
$file = file_get_contents($server, false, $context);
//decode the XMLRPC response
$response = xmlrpc_decode($file);
//display the response
print_r($response);