How to Unlock Iphone 3G/3gs to use with T-mobile Pre-paid Service

Hey I would Appreciate any help on how to do this:

I need complete step by step instructions on how to unlock a brand new untouched/unactivated iphone 3g and 3gs (dont kno which im buying yet)
I want to use it with tmoblie $1/day unlimited text etc prepaid service

I have an unactivated tmobile sim

Thank You

Also if there is a thread that could help you can just give me the link please.

Thank You!