8 MB will work. Go here: http://pdaphonehome.com/forums/ppc-6...working-2.html, then, see the post below from pdaphonehome.com.

Worked for me too. Got 7.6 GB now!
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dfj4541


Posts : 1
Location : N/A
Posted : 12/11/2007 10:37:28 PM
I purchased the "SanDisk 3 in 1 Memory Kit - 8GB" (microSDHC card) from Verizon for $97.49 (with 25% business discount) before they reduced the XV6800's memory spec on their website from 8GB to 4GB. On initial installation, the memory showed only 4GB. Here are the steps I took to successfully get the full 8GB:

1. Power down the XV6800.
2. Remove the plastic tab from the memory slot and insert the 8GB card.
3. Turn the XV6800 back on.
4. Check the available memory from Start->Running Programs->Storage Card. It should show a little less than 4GB.
5. Download SDHC.777.cab.zip file from http://pdaphonehome.com/forums/666225-post41.html to the desktop PC.
6. Unzip this cabinet file to SDHC.777.cab (don't run it yet).
7. Transfer SDHC.777.cab to your XV6800 using Microsoft ActiveSync. i.e. in ActiveSync go to Tools->Options and select "Files". This will create a "WM_{user name} My Documents" directory on your PC under "My Documents". Put SDHC.777.cab in that directory then synchronize via the USB cable.
8. On the device, browse to SDHC.777.cab from Start->File Explorer
9. Select SDHC.777 to run it, confirm that you are willing to run this file from an unknown source.
10. After the install, it will prompt you to restart the XV6800, say Yes.
11. Check the available memory from Start->Running Programs->Storage Card. It should now show a little less than 8GB.

Of course, it would be easier to download the CAB directly to the device (instead of steps 5-7).