In the past I've spent a great deal of time trying to understand the different between PHP5 abstract and static classes/methods. I find out, use the differences on whatever I'm doing, and the forget. No more. I will document my understanding here to help myself, and some day others, out.
Methods (not classes) can be defined as static (eg. not static class Oliver{} but rather static function talk()) in order to call them without going through an instantiated object. From my perspective, it makes code cleaner and less messy by wrapping related functions in a class wrapper instead of defining them globally. It should be noted though, that classes with static methods CAN be instantiated, and those methods can be called either statically (via the :: double colon notation, or via the -> right arrow notation on the instantiated object).
read