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For what it's worth, my 8330 (CDMA) Curve happily uses a Transcend® microSDHC Class 6 Card 4GB (TS4GUSDHC6).
My understanding is that capasities above 4GB may have minimum device "platform" version dependancies.
It depends on the software version. I know 4.2 supports 4 gig. Before that, it does not. 4.5 will support 8 gig.
Somewhere there's a list, but I don't have that link.
Brings up the HelpMe Screen w/all the version/platform info.