Instructions on how to unlock the iPhone 4, iPhone 3GS, and iPhone 3G for use with any GSM cellphone carrier using UltraSn0w. This will work with the iOS 4.2.1 firmware on the 06.15.00 baseband.
Instructions on how to jailbreak and unlock your iPhone 3G on iOS 4.2.1 firmware using RedSn0w for Windows. This tutorial will show you how to upgrade your baseband if needed for unlocking.
These are instructions on how to replace the signal strength bars on your iPhone with a numerical representation of reception strength. (ie. numbers instead of bars)