The trick is to read out the cdata as a string first, let libxml wrap it into welformatted html and then parse out the values from the nodes containing your data.
Note that this works but assumes that lon and lat are always in the first nodes in the cdata
// the xml as a variable
$xml = '<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://earth.google.com/kml/2.1">
<Document>
<name>OpenCellID Cells</name>
<description>List of available cells</description>
<Placemark><name></name><description><![CDATA[lat: <b>3.378199</b><br/>lon: <b>-76.523528</b><br/>mcc: <b>732</b><br/>mnc: <b>123</b><br/>lac: <b>4003</b><br/>cellid: <b>26249364</b><br/>averageSignalStrength: <b>0</b><br/>samples: <b>10</b><br/>changeable: <b>1</b>]]></description><Point><coordinates>-76.523528,3.378199,0</coordinates></Point></Placemark>
</Document>
</kml>';
// read into dom
$domdoc = new DOMDocument();
$domdoc->loadXML($xml);
// the cdata as a string
$cdata = $docdom->getElementsByTagName('Placemark')->item(0)->getElementsByTagName('description')->item(0)->nodeValue;
// a dom object for the cdata
$htmldom = new DOMDocument();
// wrap in html and parse
$htmldom->loadHTML($cdata);
// get the <b> nodes
$bnodes = $htmldom->getElementsByTagName('b');
// your data :)
$lon = $bnodes->item(0)->nodeValue;
$lat = $bnodes->item(1)->nodeValue;
Last not least, this is to illustrate how loadXML and loadHTML differ and how to use that. As for googleeart kml, I am sure that is a more standard way to parse ...
