■ Windows + PlayStation 3: To play a character from each a version simultaneously
- A Square Enix account
- A copy of the Windows version
- A copy of the PlayStation 3 version
*You can register up to eight registration codes per Square Enix account.
*Please create separate service accounts for the Windows version and the PlayStation 3 version of FINAL FANTASY XIV. You will not be able to play at the same time if you register the codes under the same service account.

I found this information but I'm slightly confused. Does this mean I would still have to pay more money as if it was a separate account? Am I able to pay the monthly fee for one account while multiple characters are able to play?

I doubt this would be possible since it doesn't seem likely for a for-profit business. xD Somewhat hopeful however.