The ClearBoost's boosting capability comes from a stubby antenna that extends from the top of the case. It's only half an inch tall and is covered in a rubbery material that extends partway down the back of the phone. Inside the antenna is a copper wire for catching the signal. The wire extends down the interior of the case to a large coil at its bottom end. The coil is designed to make contact with the iPhone's internal antenna.
The ClearBoost works best in places where you have two or three bars of reception. In those instances, we noticed we got an extra bar (and rarely an extra two) after we snapped on the case. The change wasn't noticeable immediately, but we did get the extra boost after a few seconds. A better test however, is to use your iPhone's "field test mode." To get there, type "3001#12345#" into the your iPhone's keypad and press the Call button. In the top right corner of the screen you'll notice a dBm number (basically, decibels per milliwatt) that represents the signal strength that your phone is receiving. The lower the number, the better the signal.
During testing of the ClearBoost, our dBm number dropped much of the time, particularly in the aforementioned places where we had some reception to start. The effect wasn't always detectable, but the number did indeed change. When the clarity improved audibly we noticed less static and fewer cut-outs, but our callers' voice quality sounded about the same.
When we had just one bar, however, the ClearBoost made no noticeable difference. The bars and dBm did not change significantly, and we didn't notice any audible improvement in our calls. We tried the ClearBoost in a few places with poor reception and had the same result each time. That is really too bad, since those are the moments when you'd need the ClearBoost most. Conversely, on places with great reception the ClearBoost didn't make a difference either. But that doesn't upset us since the quality in those areas was good enough in the first place.
