The main differences are:
- The font name has changed (language-specific)
- The font type has changed (CCC or TTF)
- The font location has changed
If you are an experienced font hacker, then the short story of how to change the fonts is:
1. Create a TTF font, and change the "full font name" embedded in the TTF font to "Sans MT 936_S60". You need a TrueType Font editor to do this, like this one. Note that this font name applies to Chinese-input version of the phones. It is likely that English-only phones will use a different font name.
2. Copy the TTF font file to your memory card, and place it in the directory "\Resources\Fonts\". Create the directory if it does not exist.
3. Reboot the phone and it should use your new font.
4. If you want to change back to the default font, just delete the new font file from your memory card "\Resources\Fonts\".
P.S. I have since sold my N80 so no more updates on this article.