Hey, iPhone 3G owners: Please do not download the 2,1 firmware files listed below. They are for the 3G S and will not work on your phone. Read the whole post for details. The correct firmware for the 3G will start with "iPhone1,2" instead.
If you were up all night waiting for the new iPhone OS to arrive, you're in good company -- we were too, until we began getting Twitter reports from users in Hong Kong and Sweden that the local carriers sent out SMS alerts to their customers suggesting when they could download 3.0. Those times both align with a 10 am PT/1 pm ET go time, and that's when we're calling it for now; Engadget concurs. That's why you're still seeing 2.2.1 as the most current version in iTunes; the new version hasn't been released yet.
Those with a command-line bent and an inability to wait without doing something can launch Terminal and type in the following every few minutes to see whether 3.0 has launched, rather than repeatedly clicking the Check for Upgrade button in iTunes (note that the up-arrow in Terminal reloads the previous command):
curl -s -L http://phobos.apple.com/version |\
grep -i restore |\
grep '_3.' | open -f
The results will look something like URLs ending with this:
The model number indicates which unit has downloadable firmware. As of right now, only the iPhone 3G S firmware has been updated. That's the 2,1 iPhone model. Yes, the 1,2 iPhone 3G model was considered a revision of the first generation 1,1 iPhone as it only had moderate hardware changes. The two iPods are 1,1 and 2,1 for the first and second generation.(No, for those wondering in the comments, you cannot download the 2,1 firmware and install it on your iPhone or iPhone 3G -- it will only work with the 3G S.)
To download, copy the URL and paste it into Safari's download window or use any other favorite method to retrieve the firmware. Then hold the Option key and click Update in iTunes. Navigate to the firmware (the ipsw file), select it, and 3.0's good to go. Of course, you can also download directly through iTunes as soon as the update is available.