I'm selling my fiances 3GS with 4.2.1, never been JB'd. The guys wants it with the stipulation that i JB and unlock for him. I've done it a bunch of times for people. But what i wanna know is should i just leave the 4.2.1 on it, or upgrade it to a newer version, and then JB and unlock? If so, what version should i upgrade it to? And the best tool for unlocking would be what?