Unlock iPhone 3G yellowsn0w

"Unlock iPhone 3G yellowsn0w", The Dev Team has released yellowsn0w, the 3G iPhone unlock. Its available NOW via Cydia, you'll need to add their source (check the release post for the URL - they'd prefer sites didn't link the repo url) then check your Changes tab - yellowsn0w should be right on top. If you don't know how, here's how to add a source in Cydia.

Refresh if you don't see it. If you're reading this later, just search for yellowsn0w in Cydia (making sure of course you've added their source). As guessed (and confirmed a bit later) from their post earlier today, IT WORKS WITH THE 02.28.00 BASEBAND version - in fact, ONLY for that baseband version. Meaning yes, you will need to update in iTunes and then use PwnageTool on a freshly updated 2.2 iPhone if you DON'T have 02.28.00 right now. Running the unlock on older basebands will simply cause it to exit, and do nothing. "No harm, no foul."
All you do is go to the package in Cydia and install just like you'd install any other package. Boom - restart the iPhone, and...

...wait for the slide to unlock screen, then wait 10 or 15 secs more. If you don’t see your carrier name pop up, then remove your SIM, reinsert it, and wait 10 secs more. This is the step we’ll be working on eliminating next.

Then you're unlocked. A quick note for users whose SIM cards come preinstalled with menus or apps on them, you'll

...need to pull and reinsert the SIM once after rebooting the phone to engage the unlock. Even though it’s needed only once per boot, it’s still a nuisance and we’ll be fixing that ASAP... You’ll know if you fall into that “extra step” category if your carrier doesn’t show up within about 10 seconds of the slide to unlock screen.

There is a known issue with SIM cards that have STK (SIM Toolkit) application menus, these menus are usually items such as “top up” “get credit” etc. These menu items confuse the application sometimes, removing and reinserting the SIM fixes this issue.