CTIA IT 2006 --SanDisk has again upped the ante and doubled previous capacities of the miniSD card. The new 4GB card is called SDHC because it uses the FAT32 filesystem which is "High capacity". Unfortunately, today's mobile phones run with the FAT16 file system and thus are unable to work with the new cards. SanDisk said that a firmware update could add the new functionality to existing handsets and that models supporting the filesystem are expected to ship in the near future. The technology is backwards compatible so handsets can make use of both miniSD and miniSDHC cards.
Because of limited device compatibility, SanDisk is not currently marketing the new miniSDHC cards at retail. They are being shipped to phone manufacturers and OEMs. HC technology should make its way to microSD in the future as well, upping that technology's maximum past the 2GB level that it's at today.