There is a way to learn how to unlock iPhone 3g without sim card for those who desire to use the device on other networks. First, open up the iTunes program that is on the computer you generally sync the iPhone with. Go through the menu bar to check for updates. This will ensure that you have the most up to date version of the iTunes program available.
Once iTunes is updated connect the iPhone to the computer using the USB cable. Press the power button on the iPhone and then slide the bar to unlock the screen. Go to the “settings” menu on the iPhone and under the general tab press “about.” This will give you the operating system your iPhone is using. Now download the blackrain jailbreak software that corresponds with the operating system of your phone.
After downloading Blackrain to your computer click on the new icon. When Blackrain opens it will be in a small box and you should click on the button that says, Make it rain.” And then you will click “ok.” The process will last about 5 minutes, but the iPhone will automatically go into recovery mode and then it will automatically restart. Press the new Blackrain icon that has been placed on the screen of the iPhone. Select the “Cydia” and “snow” packages. These will take about 5 more minutes to download and install then the iPhone will restart which indicates the process is completed.