Tested by me!
Restore with original 3.1.2 firmware
Install Blackra1nRC3
Install cydia
Go to Cydia and search Bootneuter
Install..
Desactive keyboard lock ( put in NEVER )
Wait.... a fell minutes
Enjoy your iPhone 2g unlocked
More details...
http://ihelplounge.typepad.com/ihelplounge/2009/11/how-to-jailbreak-unlock-iphone-2g-312-firmware-with-blackra1n-rc3.html
download link original firmwares....
http://unlockiphone2g3g3gs.tuningblog.com.br/7705/Lista-completa-com-todos-firmwares-para-iphone/