I had a 3GS early model that was not jailbroken, had iOS 4.2.1, needed it unlocked and untethered JB so I did the following:
1. Jailbroke and updated baseband to 06.15.00 (iPad baseband) with redsn0w 0.9.6 rc8 (tethered).
2. unlocked with ultrasn0w.
3. re-jailbroke with greenpois0n (windows) on...