December 31st has been and gone, at least where I'm sitting, and right now there's still no yellowsn0w iPhone 3G unlock from the Dev-Team. The group of Apple hackers had previously promised a version of their baseband unlock tool on New Year's Eve, but that has seemingly been delayed.
Before you get too frustrated, though, it sounds like it may be worth a few more hours: over the past few days, the Dev-Team have managed to add support for the latest iPhone baseband, version 02.28.00.
"The soft unlock has undergone many changes in the last two days. The most significant one: the soft unlock will now be only for baseband 02.28.00 (the most recent baseband). Yes we’ve been advising everyone to avoid updating their basebands, and in general that will always be the best policy. Not every baseband version is guaranteed to have a hole through which we can inject the unlock" iPhone Dev-Team
Previously iPhone 3G owners hoping to unlock their devices had been warned not to update to Apple's latest baseband firmware, as it was not expected to be addressed by yellowsn0w. In something of an about-face, the Dev-Team are now saying that only 02.28.00 will be supported by yellowsn0w.
Right now, the full release package is waiting for a file permission error to be corrected; once that takes place (i.e. when the team member responsible wakes up), it will be distributed. Some iPhone users with SIMs that contain menus and apps may find an issue whereby the carrier isn't found at handset boot; a temporary workaround is pulling the SIM and replacing it, but the Dev-Team are working on a fix.