Internet Doesn't Work via 3G on iPhone 4

To resolve 3G connectivity issues on your iPhone 4, first ensure that Cellular Data is enabled in Settings under General and then Network. If it is already on, you may need to manually configure your APN settings, especially if the device was recently unlocked or used with a different carrier. You can also try resetting your network settings by going to Settings, General, Reset, and selecting Reset Network Settings. This will clear saved Wi-Fi passwords but often restores a lost data connection. Finally, verify with your carrier that your data plan is active and compatible with the iPhone 4.