Informacion bastante util:
I just spoke to a very helpful customer service agent to further clarify the situation on how the different accounts work and preorder works. Some of this information is buried into other threads, but I wanted to create one to clarify this for those who are still confused.
Management and Social Accounts don't need to be linked. The game you pre-ordered is not tied to an account until you enter the code, either via the Client or the secure Management Account site. The only one that matters in the end will be your secure Management Account.
The Pre-order code is simply a code to get another code via email. Yes, it's pretty silly and kind of dumb. This site is not working 100% properly at this time. The social account is almost irrelevant. For NA, preorder.na.finalfantasyxiv.com.
This second 20-digit code is the one you will enter via the client at the start of Early Access. Edit: (via StretchMarksGG) You can also enter the code on the secure Management Account, as detailed in http://support.eu.square-enix.com/faqarticle.php?id=5383&la=2&kid=67923&ret=main. (EU site but once you login it doesn't matter, your in YOUR account management.)
There will be another code at launch, which I assume activates the 30 free days and such. As he described it, this will create the "full service account." Don't get bogged in the names, but that's basically saying the game will be activated on whichever account you enter the code on.[/i]
Fuente: http://www.reddit.com/r/ffxiv/comments/1kryrr/clarification_on_social_account_management/