Kindle 3 Font Hack Lite
Font Hack Lite is a way to use change reader fonts without have to hack the Kindle
The is for Firmware 3.x and 4.x only.
It's not as complete/powerful as the full hack, you'll only be able to change the reader font, exactly the same way as the official font switch in the [Aa] menu. The full hack can be found at: Kindle Font Hack for all 2.x and 3.x Kindles
 The steps
First, make sure your Kindle is on the Home screen before plugging it to your computer.
You'll have to edit the reader config file, which is located, once your Kindle is plugged to your computer, in the system\com.amazon.ebook.booklet.reader folder. (Att, Windows users: depending on your Windows Explorer settings, this folder might be hidden. To workaround this without messing with Windows Explorer settings, just enter the folder name in the address bar). Once you're there, open the reader.pref file in your favorite UNIX-aware text editor. (Yes, it's the same file where you can tweak the horizontal margins)
In there, just before the
and replace the FONT_FAMILY= line with:
Once that's done, we'll have to put our custom fonts where the Kindle expects them...
In the root of your Kindle, create a folder named fonts. In this new folder, you'll have to put your custom fonts with very specific names, according to their style, kinda like with the Fonts hack.
Regular: alt-Regular.ttf Bold: alt-Bold.ttf Italic: alt-Italic.ttf Bold Italic: alt-BoldItalic.ttf
And that's it! Eject your Kindle, and Restart it. (Or, if you can, just restart the framework).
You Kindle should now be using your custom font instead of the usual Serif/Serif Condensed/Sans Serif.
As always with this kind of tinkering, it won't survive if you try to change this specific setting (font choice) in the [Aa] menu. But every other setting (ie. font size) in the menu should be fine.
On a sidenote, Amazon also has user screensavers ready under their sleeves, but I haven't been able to enable this without a jailbreak... (Cf. this & that).
Note that the Kindle software now uses TrueType bytecode hinting instructions, and hint at the strongest level possible. (In terms of FT/FC settings: hintstyle=hintfull, hinting=true & autohint=false).
OpenType CFF fonts work fine too, without converting them
Many thanks to NiLuJe.
Note: Amazon does not support 3rd party hacks and may void your warranty should anything go wrong. Exercise caution and use at your own risk. Only the user will be responsible for the results (good or bad).
 For more information
Please visit NiLuJe's Changing the reader font without a hack [K3] on MobileRead.
WARNING: Use at your own risk! This is an UNOFFICIAL update to allow custom Kindle Fonts. This file is NOT from Amazon.com and any harm it causes your Kindle will be your own fault.