Lately, I've been noticing HUGE variations in the signal strength on my iPhone 4. It goes from 1 bar to 5 bars and back to 1 bar over a short period of time sitting in the same place. At home too I have been noticing such variations...previously I always had 3 to 4 bars. Today, I went by the Apple store and my phone had variable signal between 1 bar and 4 bars. An employee there had an iPhone 5 with 4 bars at the same time that mine showed only 1 bar. Is the phone failing? Or has something been changing with AT&T's network?