My iPhone 4 has an E on top of it instead of 3G?

I have my iPhone unlocked to T-mobile. Someone told me it stands for edge speed. What does this mean? & how can I get 3G Speed?

E and 3g are very similar, you shouldn't worry about it.

That E is the original internet connection. Edge network. It is slower than 3G.

Usually E is used for rural places like for example I travelled to the middle of nowhere and I got E instead of 3G. If you aren't in the middle of nowhere and you still get E you can go to settings>general>cellular>and turn 3G on.

The sign of "E" is EDGE symbol. This is a kind of internet providing system in the phones. That it's speed is double of simple and basic internet on older phones. But considering that you uses 3G network, you must be able to handle with 3g internet that have speed about 512 kbps.
contact with your phone factory and get help from them.
nothing with your phone's circuit. It just disarranged.