My bars completely disappear. Just reads "AT&T" for a minute or two and has no service. When I do have service, I'll have 5 bars. This happens everywhere, not just my home. Happens with and without my bumper and other cases.
Yeah my iPhone 4 does the same thing. I thought it was because we just got 3G service here in the Little Apple (Manhattan, KS). Our 3G service is still in the "testing stage" according to the customer service rep at the local AT&T store. Supposed to be "live" 3G August 16th.
Mine does that too regardless of whether I'm holding the phone. I just got a 3G microcell, so now my bars vary from 2 to 5 for no apparent reason. Regardless of this peculiar behavior, I have yet to have a dropped call.