In Atlus' Volume 23 of Creator Works, Persona 3 Director Katsura Hashino (also producer of the Trauma Center series) reveal videos of what the battle system looked like during the early stages of development.

Due to the fact that P3 is different than previous MegaTen games with its dynamic menus and comic-like visuals, the staff had to do quite a bit of experimentation such as how encounters should work. Initially, they tried using something that resembles a real time battle system like that used in ARPGs. You see enemies on the field and fight them on the spot. No transitioning between screens.

Nice victory dance.

This actually reminds me of all the Korean MMOs I've tried out so far such as RAN Online and RF Online. Amusement didn't last long because all I found myself doing was bashing buttons and killing everything in sight so, I'm glad Atlus didn't end up using the system they show here. The final system they use in P3 might not seem that different but at least there's an incentive to plan in battles before each move.

However, due to the limited amount of memory the P3 team had to work with, they decided to try out the common way RPGs work i.e. switching to the same battle screen for (almost) every encounter. This video shows you something a little closer to what the finished product looks like.

Closer to the finished product.

Katsura will continue talking about the work they put into developing the game system in the next volume of Creator Works. Meanwhile, you can checkout previous volumes for some screenshots taken during development.

Also didn't know Atlus has a Persona game planned for the PSP since 2004. I wonder if it'll just be a port / remake of the first PSX Persona game "Revelations: Persona" or, will it be something original? I really hope for the latter because I'm getting kind of tired of all these remakes that have been coming out. Even better if it's something as good as P3.

前に発表されたPSPのペルソナゲームがペルソナ３ほど良いのオリジナルゲームだといいな！（’　▽　’）ノ