I currently have my new iPhone 4 in a MiLi PowerSpring case/battery and since using the MiLi no more reception issues. My wife, however, hates using a case and she continued to have issues with signal dips. It took me less than a minute to fix her phone using clear tape and an Exacto knife. I simply covered the bottom left corner of the metal antenna band with clear tape and used the Exacto knife to neatly trim the tape. Problem solved! You can't even see the tape and she gets 4 bars no matter how much you hold the left side of the phone. Apparently the issue has nothing to do with covering the antenna as much as it does using a non-conducting material near that bottom left corner joint of the phone. All Apple has to do is ad some sort of durable clear plastic coating to the metal band.