I've just bought a couple of accessories for my Pocket PC. I got the official Hewlett Packard USB combined cradle and charger and a 256 MB Secure Digital card, both from eXpansys UK (recommended). Unfortunately all is not well.
I bought a nice capacious SD card so that I could copy some of my MP3 collection to it but even this isn't straightforward. I assumed that the ActiveSync software would have the intelligence to automatically start filling the storage card once my MP3 files had used up the internal memory (or at least offer this as an option) but alas, no. No problem I thought, I can use my universal media reader to copy the files to the card directly in one hit. This worked fine at the Windows XP end and the card showed up as a removable drive formatted using the FAT file system. However when I inserted the card in the h1910 it prompted me to format it. I guessed that formatting it on the Pocket PC would sort things out and tried copying the files directly again. It didn't work.
It appears that you have to use the internal RAM as a buffer, synchronising a few files at a time from the desktop PC to the h1910 and then using the Pocket PC File Explorer to move them to external storage.
If anyone knows a way around this ridiculous limitation then I would really love to hear from you!