PHP 5. 2 will be retired from the primary web server on Saturday, September 3, 2011 at 12 AM EDT (-0400 GMT) in accordance with its end-of-life announcement in July 2010. After this time, PHP 5.3, which is the currently recommended version, will be promoted as the primary PHP interpreter. Those whose sites are not compatible with PHP 5.3 may delegate page requests to the secondary HTTP server that will continue to run PHP 5.2 until at least March 2012.
As we near a transitioning point, tools will become available within the control panel to facilitate a fallback to PHP 5.2. For most sites this will be a seamless transition.