Manfred Webber, after reading an article from PHPBuilder, decided to show a "more standardized" method for communication between PHP and a Flex application. In his latest post, he shows how to use the PEAR Services_Webservice package to help make the connection.
Why not do the same with Flex and the PEAR package Services_Webservice which I think is a smarter way, if you want to use XML at all. Smarter because you use Web Standards and developers do not need to learn and parse the returned XML structure.
He includes both the PHP code for the web service and the cut&paste for the simple Flex application.