In this tutorial, we learn how to unlock the iPhone 3G to work on other carrier networks. First, purchase an ATT Universal unlock SIM card and cut it so it is the same size as the SIM card in your phone. Don't cut any important parts off the back of the card. Now, remove the card from the iPhone and install the Universal unlock card. This is all you have to do and now you can run your iPhone on a different network. This is the most simple way to use your phone on another network. You can reset functions on your phone to work with your carrier and adjust different preferences.