In recent weeks, several iPhone unlocks have been released and detailed. However, this latest release will likely interest the most, as it is the first to both be easy to install, and free.
Unlock.app is a tool that, once copied to an iPhone, executes all the steps necessary to SIM unlock the device. After being unlocked, it can be used on any compatible carrier, such as T-Mobile in the United States. To help assist with downloading the tool, we have made it available for download from our servers at the bottom of this article.
We have tested, and confirmed that the tool works. However, it is a bit unstable, and we suggest you view discussion in the forums for best results.
iPhone Unlock Tool (See site above for instructions)
Update: A newer tool, anySIM, has been released. This tool builds on the above tool by adding stability and a better GUI. You can download anySIM here from our servers.
Update 2: Installing anySIM will prevent your iPhone from being upgraded to iPhone software version 1.1.1. If you have already installed anySIM, do not upgrade to iPhone software version 1.1.1.