Special thanks to Serge A. Levin for updating my 3.2.1 jailbreak to remove the need for precise timing. It can now work as any other jailbreak. Just read and follow the directions in README.txt, or for your convenience:
1) Copy and paste the correct update for your device
k2 = Kindle 2 US
k2i = Kindle 2 International
dx = Kindle DX US
dxi = Kindle DX International
dxg = Kindle DX Graphite
k3 = Kindle 3 Wifi + 3G (US & Canada)
k3g = Kindle 3 Wifi + 3G (Elsewhere)
k3w = Kindle 3 Wifi
2) Go to the Settings page via Menu -> Settings
3) Select “Update Your Kindle”
This should in theory work with every Kindle version from 2.0 to 3.2.1. However, only Kindle 3 on 3.2.1 have been tested, so use at your own risk.
If this doesn’t work for your older version Kindle (< 3.2.1), try the 0.4 version which supports all Kindle 3.1 and below.