How Can I Unlock My iPhone 3G?
If you're interested in using your iPhone 3G with any GSM mobile carrier the iPhone Dev-Team has the answer. Unlocking can also save a few bucks if you have AT&T and you're using your iPhone 3G outside of the US.
Using the latest release of ultrasn0w simplifies the process, but will only work with the iPhone 3G. Start out by making sure your iPhone 3G is updated to iPhone OS 3.0 and jailbroken with PwnageTool or redsn0w. T-Mobile users should disable 3G on their device.