The mis-named iPhone Configuration Utility (it works for iPad and iPod touch too) is Apple's free tool for managing Enterprise iOS features. These features are often otherwise hidden from the UI. iPCU functionality is included in Apple Configurator, but the main advantage is that works both in Windows and Mac.
The current version is 3.5.
Configuration profiles created in iPCU 3.2 function only with iOS 4.2 or greater. This excludes iOS such as the original iPhone and iPod touch, which are limited to iOS 3.1.3.
The canonical reference for the mobileconfig file is in the Apple Developer Library: iPhone Configuration Profile Reference.
Information on changes between releases is available at iPhone Configuration Utility Tech Note.