Help? 3G jailbreaking/unlocking problems!

[Atokadd]

I bought a brand new iphone off ebay a day ago.
A 3G, and im trying to unlock and jailbreak.
Its firmware is 3.1. Im using Pwnage tool 3.1, and when i make a custon ipsw. file, it never works. Either i get the "Error 1015" or I get in, but when I actually go to unlock from Cydia using ultrasn0w, it works fine, I disable 3g, but when i reboot my phone, it just says "searching.." than eventually "No service."
Yes, my sim card is in.

I would really like some help guys, my parents will murder me if I cant go it right.

[satch2501]

Error 1015 usually happens when you are trying to install a custom firmware on a phone that's already been pwned. Put your phone in recovery instead and install the custom firmware. Once the process is done, set up your phone as a new phone not from a backup. I had the same problem and by setting it to "new phone" in itunes, and installing ultrasn0w (although I am on a legit carrier) it worked.