Taken from lodestone:
Welcome Back Campaign
For those of you who have applied the registration code of FINAL FANTASY XIV Version 1.0 before Saturday, September 29, 2012 can play for free until September 9, 2013.
* Starting September 10, 2013, players will be required to pay a subscription fee.
So, it's not a month, my apologies, more like a week or two.
Edited, Aug 19th 2013 8:16am by RyanSquires