First you’ll need to download the last version of Android, 4.03 right here. This will step you up to build V11R42A.
I think you need the ‘version upgrade package‘, although I wound up kicking it via the bootloader. Also you have to unzip the 600+MB download, and place it on a SD card on the phone. Even though the image will fit into RAM on a zapped set, it’s really picky about reading it from flash.
Now because I’m not in Japan, I had to kick the installer off by shutting down the phone, then turning it back on while holding down the menu & back buttons on the phone.
Granted Android 4.0.3 isn’t exactly modern, but it’s a lot better than 2.3! And for what it’s worth, it sure feels a lot more solid after the upgrade.
Having used the phone after the upgrade, it’s faster and the battery life is VASTLY improved. If you are unfortunate to have owned one of these phones (or feel unfortunate at it’s 12 hour max lifespan) do yourself a favor and upgrade!