The Price: $29.99
The Verdict: It works, but only under specific conditions. Here's what the numbers mean (highlighted lower numbers closer to 0 are better). When you're talking with the phone up to your face, having the ClearBoost on it increases the signal quite noticeably. An increase of 3 dBm doubles the amount of "RF energy reaching the iPhone's built-in antenna," which means that in the better reception spot, the case increased that energy by a little over four times. In the slightly worse spot, it increased it about four times.
We saw the opposite effect when we placed the case on a desk and didn't touch it. A real world scenario is if you're talking on a Bluetooth headset but not holding your phone. In the better reception area, the case just barely degraded the signal, and was close enough to call a statistical tie. In the slightly worse reception area, it actually degraded signal by four times when placed onto a desk.
Here's why we think the ClearBoost works. When you're talking on your iPhone with the phone held up to your face normally, your hand is covering up the antenna on the phone—which is inconveniently designed by Apple to be located on the bottom, behind the black plastic area. The Clearboost helps eliminate that problem by essentially "moving" the antenna to the top where your hand isn't. When the phone is on a desk and your hand isn't covering the standard iPhone antenna, at best there's no benefit, but at worst it actually degrades your reception.
In the interest of completeness, we wanted to see how the reception was if we held the phone up to our face without the case, but holding the phone gingerly at the top, trying not to cover up the antenna. As we thought, reception was better there than when we held it "normally", but slightly worse than when we were using the case. It's super inconvenient to hold a phone like this, however, and isn't really feasible to do much of the time.
The Aesthetics: It's a decent enough hard plastic case that doesn't add too much bulk to your phone. The antenna on top may be a little protrud-y, but it's necessary for obvious reasons. All the buttons and ports are accessible, and you can dock your phone in most docks without much problem.
The Notes: One thing to note is Griffin explicitly states that the ClearBoost only works if you have your phone on the AT&T network, which uses the 850 MHz band. If you're on T-Mobile, which primarily uses the 1900 MHz band but roams occasionally onto 850 MHz depending on where you are, you'll get less benefit. We tested this on AT&T. Richard from Wireless Info also notes that the signal/noise ratio is important, and that more dBm might not mean better sound quality.
The Testing Procedure: We didn't test with how many bars the phone gets, because how many bars it gets is only a rough display and doesn't go up or down completely based on the "signal". Testing using the iPhone's Field Test app shows how strong the actual signal is in dBm, which measures in terms of amount of "RF energy reaching the iPhone's built-in antenna." Each number in the chart is an average of five to seven samples.
The Bottom Line: If your reception's no good and you often talk with your phone up to your face, the Griffin ClearBoost will give you a bump in signal. If you talk with a Bluetooth headset more often than not, you might want to skip this. At $30, it's probably too cheap to pass up. [Griffin]