The Dev Team just released an update to their UltraSn0w unlock. Unfortunately, this time it's not as easy as downloading and installing UltraSn0w to unlock the iPhone.
If your iPhone is on baseband 01.59.00, 04.26.08, 05.11.07, 05.12.01, or 05.13.04, then you can simply go to Cydia and download UltraSn0w. If you are on a different baseband, you will first have to update your baseband to 06.15.00, which is unlockable.
All this sounds a little confusing? Yes, it's normal. It's very confusing, so I highly suggest you read this before going forward with the unlock process. It will tell you what you can and cannot do, depending on your configuration...