Hit the downloads area and look for a Monster Pack that's unlocked. I'm pretty damn sure I used one there on one of my V3xx's. Just use Flash & Backup 3.09 to reflash the phone with the monster pack.
there is no "free" unlock for the v3xx unless you get the code from the origional SP(service provider)
otherwise you must buy the code from an online unlock site using the IMEI #
simply flashing unlocked f/w will never unlock a phone