Can anyone give me step-by-step instructions to unlock an iPhone 3G?

Seriously, I need a simple version.
Unlocking iPhone3G for Dummies, if you will.

I recently came to be the owner of an iPhone 3G, thanks to a friend who no longer needed his.

I have Tmobile, and I would love to unlock the iPhone and use it.
All I know about my iPhone 3G is this...

Firmware version 3.1.2 [7D11]
Modem version 5.15.04

I've tried downloading ultrasn0w and yellowsn0w.
But I really don't know what I'm doing.. So, instead of screwing up the phone, i need help!!!!...
so... Help... please?

To unlock an iPhone the remote unlock service would be a better option because,you need not give your mobile to someone else nor do you have any chance to enter the wrong unlock codes.To get such an unlocking service for your iPhone 3G approach Superunlockcodes.com and by submitting the country and network to which the mobile is locked to you will be able to remove the restriction from the respective network.This will be a permanent unlocking solution.If you are not sure to which network the phone is locked to...contact the previous owner or the customer support of the website that I have mentioned above.