Unlock the iPhone 3G

http://blog.iphone-dev.org/post/67797811/dont-eat-yellowsn0w

BASICS

* The unlock works exclusively with baseband 02.28.00. This baseband is provided by the latest firmware update (2.2) from Apple. You’ll need to upgrade to this release using iTunes and then use QuickPwn to activate etc. There are plenty of tutorials about this on iclarified, bigboss, modmi and other established tutorial sites. Because it works on 02.28.00, it is available to everyone on the planet. This means we don’t need to unnecessarily expose holes in earlier basebands, which is an important concern.
* The application is a small daemon that is launched on boot. It injects the payload at boot and also whenever there is a baseband reset. You won’t notice anything about it other than that your third-party sim now works. It’s a small program and unobtrusive. There is no GUI (this is by design).
* You can add the application using the sources outlined below. There are Cydia and Installer sources available, so use whichever you are comfortable using.
* yellowsn0w is completely removable through Cydia, the command line, and iTunes.

Source: Hacknmod