I don't know if this applies to the 3G model as well but I have discovered what appears to be a very fundamental design flaw. Ever since I bought the 3GS I noticed that the signal strength fluctuated, frequently fluctuating between a full 5 bars and a 1 bar or nothing. I tried to find the answer to this problem on various forums with some weird explanations like attaching a USB cable or a scotch tape to the sim. Nothing I tried improved this. I noticed that it seems to drop just when you made a call and recovered immediately after the call. This made me wonder if it had anything to do with how the phone was being held. Some users were saying that two identical units would report different signal strengths at the same location in the same network. Anyway after a lot of experimenting I discovered that the iPhone 3GS appears to be extremely sensitive to being held on the lower 1/3rd part of the handset. Holding the phone in the top half recovers a full signal within a few seconds (15/20 secs)!!!! You can try this yourself. Putting the phone down on the table or picking it ensuring the bottom half remains uncovered seems to work. Covering the bottom half starts to drop the signal. The design flaw is that the receiving antenna should be placed at the top of the phone which is least likely to be covered when held. Either way it's a flaw that Apple should recognize and fix. Other handhelds don't seem to suffer from this characteristic.