You can not unlock the 1.1.2 OBT phone. You can house break it but thats it.
This will not work if you the if 4th and 5th digit of your serial number is 46 or higher. In other words, if you bought your iPhone and it already came with firmware 1.1.2, then this guide will not work! Out-of-box 1.1.2 iPhones are currently (as of 11-29-07) impossible to unlock, so don't try.