Tools You'll Need: iPhone 3G , TurboSIM Card
Upon completion of these steps, you will be able to unlock and use your iPhone 3G with any wireless network carrier with your existing SIM card
1 - Locate and acquire a TurboSim unlock card. These can be found on eBay by conducting a search for 'turbo sim'. They can be purchased for around $10.
2 - Once you've received your TurboSIM card, locate the SIM Card slot at the top of your iPhone. To open the slot and remove the SIM card, use a paper clip to push the small button inside the hole on the SIM card cradle. The cradle will release and pop out.
4 - Place your new (or old) SIM card from any wireless carrier on top of the TurboSIM card so that the 6 leads that protrude make contact with the conductors on the new/old SIM card. This may require a small cut on the corner of your SIM card to make room for the chip on the TurboSIM card depending on which version you purchase. If you must make the cut, it is not a big deal since it is on the side where it is only plastic.
5 - Carefully place the SIM and TurboSIM sandwich back inside your iPhone. When your turn your iPhone back on, it will tell you that you have no service. Wait a couple of minutes and let the TurboSIM do its job. After the couple of minutes, the message will go away and you'll be making calls on whatever wireless carrier you choose!