Unlocking problem.

[tissa123]

I have a Apple iphone 3G, Model: MB704LL with Bootloader 5.08, Running ISO 4.2.1 with Baseband 05.15.04. I want to unlock the phone downgrading to any unlocable ISO and Baseband.As the phone has Bootloader 5.08 i know i could downgrade the phone by using Fuzzybavd. But I dont know how? So Please please give me some instructions.Plese wite the applications name to jailbrake.thank you