Facetime 3G Setup Instructions (Via 9 To 5 Mac):
- Jailbreak your iPhone 4 via http://www.jailbreakme.com/.
- Download and upgrade to the latest Cydia package.
- Open Cydia, Go to Manage then Sources.
- Click Sources, Edit then add: http://apt.modmyi.com/
- Search for "My3G" -- download, and install it.
- Go through the Rock setup process with a username and password. Open My3G and leave all settings on the default.
- FaceTime should now work over 3G! -- Make sure to "Forget" the WiFi network you are on (via iOS settings) if you want to test it.
Try it at your local Apple Store! :)