Phases one and two of beta testing will be PC only, while PlayStation 3 testing will begin in phase three. Players will need to begin beta testing with new characters, which will be wiped at the end of phase three. From phase four onward, characters and such will continue on into the official game (barring the need for data wipes for unforeseen reasons).
Folks who applied for the alpha test don't have to reapply but aren't necessarily guaranteed access to the beta. Legacy campaign members can participate in the beta from phase one without application but should apply specifically for the PS3 beta tests if they want to go that route.
To see the ins and outs of eligibility, take a look at the system requirements, or scratch the itch of general curiosity, check out the game's beta information page.