http://support.jp.square-enix.com/faqarticle.php?kid=67224&id=5382&la=1

Can friends and family play simultaneously if they are on different accounts?

Yes, but the requirements differ depending on what platform you use.

■ Windows only: To play three accounts simultaneously
- Three Square Enix accounts
- Three copies of the Windows version
- Three PCs

■ Windows + PlayStation 3: To play an account from each version simultaneously
- Two Square Enix accounts
- A copy of the Windows version
- A copy of the PlayStation 3 version
- A PC
- A PlayStation 3 console

■PlayStation 3 only: To play 3 characters simultaneously
- Three Square Enix accounts
- Three Sony Entertainment Network accounts
- Three PCs
- Three PlayStation 3 consoles


....surely you don't need 3 PC's to play 3 characters simultaneously on PS3 right? :P