Till we get a procedure for flashing from the SD card, here's what I know works for the f900:
1) Download the Acer upgrade ROM from the acer ftp site (
ftp://ftp.acer-euro.com/smartphone/f900/os_images/), get the appropriate language file (EN for english)
2) Run the upgrade program, but add the -a command line option. This will cause it to put the files on your local hard drive.
3) Find and replace the temp.dat file (in the TempFolder directory) with the new firmware file. (temp.dat)
4) Run the PDAUpdate.msi file (it's in the parent directory of the temp.dat file).
5) connect the F900, and select ActiveSync mode when prompted. (be sure to have activesync installed on your PC!)
6) Go back into the TempFolder directory, and run the EUU.exe file
7) Follow the instructions, and the phone should be updated.
I'm SURE there's a more simple way to do this, but it's the only one that I've found so far!