Why doesn't 3G work on my iPhone?
There is a small chance you have no enabled 3G. To do this
follow these steps. Go to Settings > General > Network and
Enable 3G should be set to on. Also your area may not have 3G
capabilities. In this case there is no 3G signal for 3G to work. To
check 3G coverage contact your provider. Also if your iPhone is a
1st Generation and not the iPhone 3G you do not have 3G
capabilities.