Before Crisis is a cell phone game (that you can't play unless you live in Japan or have a Japanese cell phone). I say if you want to play Crisis Core, play Crisis Core. Get the PSP. Since it is more expensive, get that one out of the way first.

Then get the DS. You have a job (albeit a summer job), why only get one system? If you can spend $300 (for both systems, brand new) over the summer, I think you should get both.