In what can be seen as perhaps a first for the PlayStation 3, Atlus is going to be applying a region lock to Persona 4 Arena on that console. This means that even if you import a Japanese copy of the title early, it will be unplayable unless you have a legitimate Japanese PlayStation 3.
While this is unfortunate, the fact that Persona 4 Arena is already confirmed for localization and is meant to be released within a couple months in America this isn’t too much of an issue. However this is very damaging to European fans of the game as currently no PAL localization has been announced.