There're thousands of threads about it across GBAtemp.. click Search up there, or simply Google it.
I can tell you now, the (E) version, released as "Kingdom_Hearts_Recoded_EUR_CRACKED_NDS-SUXXORS", is cracked so that it works on all flashcards (except, from what I know, the DSTT, which can be fixed).
Find the cracked (E) version if you want to play it.