yellowsn0w is the soft-unlock version for iphone 3g, set to be released to public on new year's eve ... hehe, good good. been waiting for it for so long, then i can subscribe to 3g unlimited data package already! 
here's the release from their blog
"3G Unlock
We have been working hard on a few other things. The main one being the 3G unlock codenamed “yellowsn0w”. This is now completed and is currently being packaged into a user-friendly application with the simplicity that you see in QuickPwn or BootNeuter.
    * The target release date for the unlock is New Year’s Eve 2008.
    * This unlock method is available to iPhone 3Gs that have 2.11.07 baseband or earlier, we did warn you.
    * You can tell what version baseband you have by going to Settings->General->About->Modem Firmware
    * The unlock requires a jailbroken 3G iPhone.  It’ll be installable via Cydia and so it doesn’t matter if you have a Mac or PC.
    * Please refrain from updating your baseband, regardless of what version you’re at.  We’ll have complete directions on New Year’s Eve.
    * We’ll stream a live demo of the unlock before Christmas (see the update at the end of this post) "
from 
iphone dev-team blog