If the namespace is nested in the xml, then you will have to loop over the nodes.
<?php
$xml = <<<XML
<?xml version="1.0" encoding="UTF-8"?>
 <people xmlns:p="http://example.org/ns" xmlns:t="http://example.org/test">
   <items>
      <title>This is a test of namespaces and my patience</title>
      <p:person id="1">John Doe</p:person>
      <p:person id="2">Susie Q. Public</p:person>
      <p:person id="1">Fish Man</p:person>
   </items>
 </people>
XML;
$sxe = new SimpleXMLElement($xml);
foreach ($sxe as $out_ns)
{
  $ns = $out_ns->getNamespaces(true);
  $child = $out_ns->children($ns['p']);
  foreach ($child as $out)
  {
    echo $out . "<br />";
  }
}
?>