This is a complete tutorial to unlock your iPhone 3G baseband with Ultrasn0w in order to use any Sim card on your mobile. There are different steps you may have to follow in order to achieve the desired result, but currently iPhone 3G is fully exploited and you will be able to use your iPhone 3G with any carrier worldwide at the end of this 'how to'. Please remember that you are doing this at your own risk: we are not responsible of damage to your hardware or of data loss. Make a full backup of your data before continue.
Open 'Setting' application on your device, 'General', 'About' and read the 'Modem Firmware' version to identify the baseband of your iPhone 3G. Then click on the corresponding button below to show the custom step-by-step guide.