Getting Edge when everyone else has 3G

Hey guys,
I just got a new iphone4. At first I was always getting 3G, but in my school I would get edge, I guess the signal was too weak for 3G, but then I noticed that two of my friends who also have iPhone4's has 3G. My friend told me to switch it to airplane mode for a few seconds, and when i switched it back, that worked, and I had 3G. But now, I ALWAYS have edge. Anywhere. And they still get 3G. My friend said to take my phone to the apple store becuase my antenna might be busted. What do you guys think?