When I first got my phone I was getting three 3G bars in my house. I ran into some text message problems (took 15minutes for text to get to my phone) and called up AT&T. They did something with my connection because afterwards I got no 3G and 4 bars of EDGE. Flash forward 2 weeks, I run into another text message problem. Called them up again and some guy reset my connection or something along those terms. My signal went back to what it used to be and sometimes better than before.
Moral of the story: Call AT&T and have them check your connection.
Also I lowered my routers frequency in my house. Don't know if that has anything to do with cell phone interference but since it has no negative impact on wifi connection I gave it a try.
Well I reset both mine and my wifes network settings and it stays 3G until the screen goes into sleep mode. When I click on the home button it's back to edge. First time this happen since we bought them. Maybe a tower or something is down since it's both of our phones.
Mine used to do that, not sure if it does anymore, don't pay that much attention to it. I assumed that when the phone went to sleep it reverted to edge to save battery. No need to be in 3g if asleep. I noticed that whenever I brought the phone out of sleep it would show edge at full strength and then switch to 3g after a few seconds.