ar_lo_826

yah, I think his main question is to unlock the phone not just to jailbreak the phone.  There isn't any quick jailbreak out there that does unlock as well for 3gs and as goodweather said, you will need to have os 3.1.3 with the old bootrom.

Have a look on this article here:
http://www.redmondpie.com/unlock ... 3gs-with-blacksn0w/Unlocking your phone using blacksn0w

Please note that you will HAVE TO jailbreak your phone.  Try http://blackra1n.com/ (for 3.1.3 with old bootrom).