here the links 4 you guys in need - I just upgraded to 06.15.00 10 min ago and unlock works fine!
BUT READ THE WARNINGS BEFORE YOU TRY ;)
read the hole thing:
jailbreak and update to iPad Baseband 06.15.00 (yes for the iPhone):
http://www.techsliver.com/pc-users-unlock-guide-iphone-3gs-3g-redsn0w-096b5/
unlock:
http://www.techsliver.com/unlock-iphone-3gs-3g-unlock-baseband-51402-ultrasn0w/
EDIT:
GPS ON IPHONE 3GS DOESN'T WORK ON BASEBAND 06.15.00 AFTER JAILBREAK AND UNLOCK!!!
MobileTerminal is buggy on OS4 - means it crashes on startup, but here's the fix:
http://www.techpetals.com/install-mobile-terminal-4.26-for-ios-4-4.0.1-iphone-4-3gs-ipad-3.2.1-1803