Rowan:

Persona 4: Arena Is Region Locked, But The Online Servers Are Global | Siliconera

As far as I can tell, the discs are region locked, but multiplayer is unaffected. So Japanese/Europeans/Americans can all play together. Supposedly they region locked it because both games have English and Japanese text/voice, and they didn't want Japanese importing the American version at really low prices with their super strong yen.

It's out Sept. 7 in the EU, but there's no date listed for Australia. Do they tend to be within close proximity of each other.

I'm looking forward to P4G too, but they're such different games, haha. Get both?