Originally you had to register with the Square Enix Members site with the code that came with FFXIII, then they gave you another code, which was used on the SE Account site to give asuran armlets, which this code was also suppose to double as a way to get into the PS3 beta.

I am guessing when they actually have PS3 beta sign ups you have to enter that code that got you asuran armlets which will get you in. Then when it starts SE will send you a 12 digit PS3 code to use on the store since all betas are downloaded through the store.