Want to liberate your iPhone 3G or 3GS from the shackles of your carrier. Here is a new trick from the iPhone Dev Team. The team has
released a new version of its Pwnage Tool. The new version uses the 6.15.00 baseband from iPad firmware. Since iPhone 3G and 3GS also make use of the same Infineon radio chip, which is also used in the iPad, the new Pwnage Tool is capable of liberating your phone too. However, you should make sure that you are comfortable working around IPSW and SHSH blobs.
However, the Dev Team blog has listed some warnings too. Once you upgrade, then there is no way back to downgrade. This may very well result in voiding the warranty on your device. You also cannot go back to your stock firmware and in case Apple comes out with a new baseband, you would not be able to update your baseband with the fix. In any case, such change in the baseband will make your unlock non-working.
So, after reading the cautionary second paragraph, if you are still willing to take the risk, then you can go ahead and get all the instructions here. As always, we would advise you to play safe.