A friend recently purchased a 2GB SD card for his T3 ... and it didn't work in it, although it worked in my Treo 600, IIRC.
My own 2 GB SD card worked fine in his T3 (mine is an Adata 150x turbo sd card).

It turns out that the new 2 GB SD card was formatted FAT32, and mine was formatted as FAT16. The T3 handles FAT16 fine, but has problems with FAT32.

I was unable to reformat his card on either my Treo 600 or his T3 ... the FAT32 apparently screwed up the formatting attempt. So, I plugged his card into a Windows XP system, and used Windows to format it as FAT16 (My Computer : right click on the drive that is the SD card, select FORMAT ... the window that pops up will have FAT16 and FAT32 choices).

He owns TomeRaider3, so we put the 1.8 GB version of the WikiPedia on his new SD card, and it works fine on his T3.

Note: the maximum filesystem size for FAT16 is 2 GB, so check carefully before buying a 4 GB SD card for a Palm!

Note: FileZ on both my Treo 600 and his T3 incorrectly reported the FAT32 card as VFAT (well, to the extent that FAT32 supports long filenames, and is virtual, I guess it *is* a VFAT :)

(VFAT is a variation of FAT16 that added long filename support, http://en.wikipedia.org/wiki/File_Allocation_Table#VFAT_and_FASTFAT)