I really hope that it works. He hasn't yet confirmed that the card is writable to 4GB. However, the fact that the phone even reports 3875MB is a very good sign. I wasn't aware that Nokias could read FAT32.
Edit: Alright, it's obvious that the N91 can read FAT32 so I'll bet that it is very likely that other Symbian OS 9.1 models can also.