True to their word, Dev-Team announced the release of yellowsn0w, their third-gen pwnage tool, just as 2009 had its umbilical cord cut.
Currently a 0.9.1 beta, the unlock works exclusively with baseband 02.28.00 (which was part of the 2.2 firmware upgrade) — and, because it's a beta, the "use at your own risk" caveat is emphasized. Repeatedly. Issues with SIM cards and T-Mobile service are currently addressed.
Also emphasized repeatedly: Dev-Team does not take, and refuses to take, monetary contributions of any kind. They also caution against anyone taking the code and trying to sell it, with a certain "Jody" being targeted by name.
Read installation instructions on Dev-Team's blog.
Good news is that they managed to unlock the newest baseband firmware 02.28.00, their prior announcement was targeting 02.11.07
[Via the official Dev-Team blog]