Since ISPConfig 3.0.5, it is possible to use multiple PHP versions on one server and select the optimal PHP version for a website. This feature works with PHP-FPM (starting with PHP 5.3) and FastCGI (all PHP 5.x versions). This tutorial shows how to build PHP 5.3 and PHP 5.4 as a PHP-FPM and a FastCGI version on an Ubuntu 12.04 server. These PHP versions can be used together with the default PHP (installed through apt) in ISPConfig.