Those eager to carrier-unlock their iPhone 3G/3GS under the latest firmware (and only the latest firmware) have an option, if the risk of using iPad code does not dissuade them. The iPhone Dev Team has released a new version of PwnageTool that uses the 6.15.00 baseband from iPad firmware 3.2.2, which runs happily on the iPhone 3G and 3GS as a result of all three devices using the very same Infineon radio chip.
This unlock isn't for the "weekend warrior." A mistake could render your device unable to execute a full restore ever again. In addition, Apple Store employees will frown upon you if you approach them for advice with an iPhone running iPad code, and that's just the beginning. The more patient among us can wait until the team releases an official bundle.