no signal bars in an area with best at&t coverage

If you have 2.0.2 firmware on your phone, you should have good battery life with 3G - so that there is not a reason to turn it off.

The current Apple fix for the iPhone not picking up 3G in a 3G area is to switch to airplane mode and then turn Airplane mode off. Not ideal, but it works.

I have great luck with 3G until i go into an Edge area, then when I return to 3G coverage my phone will stay on Edge until I do the Airplane mode trick. I leave my phone on 3G all the time now as i see no reason to disable it - i just wish it would come back on automatically when i return to good 3G coverage area.

when 3G is not available, the phone should return to EDGE. I also noticed sometimes the phone did not return to 2G when 3G was not available. What I do: if just for calls, turn off 3G, WIFI and GPS to gain better battery power and connectivity. Use 3G only when need for faster data connections.