No, start saving your money if you want to play Final Fantasy XIII and buy a PS3. In this recent Toriyama interview (scans below, and yes, it is in english), he doesn't say a single thing about FF XIII going to PS3. What he does say, is this:
Also, we know he recently said that he loved working with PS3 and that the PS3 is an ideal console (to him) for FF XIII. So no, no FF XIII on 360 I'm afraid. But, like said above, there's still Hearesis and probably 2 other FNC-games that are still console-less. I can see one of those going to 360."In fact, the Fabula Nova Crystallis Final Fantasy XIII project isn't just limited to three titles - there are many different aspects. In terms of the formats we're reaching, as well, it's not simply exclusive to the PS3 and mobile phones."
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Source:
http://www.forever-fantasy.net/