There are several threads that discuss the SDIO but I believe the general concensus is Dell says its not SDIO. No one has ever stated they got one to work in the Axim. Yes the chipset is compatable but the slot was not wired for it to save on prodection costs. And no, no one has figured a way to make it SDIO compatable. Not sure if that answered all your questions but it should be a start in conjunction with the search ...
To get you started there is a nice thread here:
http://www.aximsite.com/boards/showt...highlight=SDIO