You can take a USB keyboard and plug it into your PS3. It is how I do all of my messaging on the PS3 between friends. It is a lot faster and easier than manually doing it.

And I signed up via the FFXIII code. So I don't know if that helps to put you into a different list or not. It is certainly not a guarantee that you'll be in the beta by just buying FFXIII. I suspect the odds do improve though.