I have a M3DS Real and it came with a GBA expansion card. But the GBA card is made for the DS Lite. I'm probly going to wait for the new DS to come out to upgrade, so would it work if i cut away the plastic on the Phat's GBA slot so it would fit??
Yes you can, but if you buy the genuine M3 expansion cart seperately you usually get the 3 extra cases (white, brown/clear and a Phat DS one) I believe that I have seen a set of cases from an internet shop but have been unable to find them again at the moment.