PHP - Convert incoming HTTP POST into variables

I'm working with a web service that is submitting an HTTP POST to a PHP page as follows:

FORM/POST PARAMETERS: None

HEADERS: Content-Type: text/xml

BODY:

<?xml version="1.0"?>
 <mogreet>
  <event>message-in</event>
  <type>command_sms</type>
   <campaign_id>12345</campaign_id>
   <shortcode>123456</shortcode>
  <msisdn>15552345678</msisdn>
  <carrier><![CDATA[T-Mobile]]></carrier>
  <carrier_id>2</carrier_id>
  <message><![CDATA[xxxx testing]]></message>
 </mogreet>

I need to be able to convert each of the XML elements into PHP variables so I can update a database. I've never had to work with an incoming POST with XML data before and not sure where to starT - I am familiar with processing incoming GET/POST requests but not raw xml.