The iPhone passed Eric L's vault test with flying colors. He was able to make very clear voice calls as well as use a data connection in the farthest corners of the vault and the iPhone never lost the signal. It always had at least 1 bar, if not 3 or 4. It did not fare so well in Eric Z's usual test, dropping his call a few times.
One thing we did notice is that signal strength is easily affected by whether the antenna is covered by your hand. If the antenna (the black plastic at the bottom of the back) is covered, voice quality seems to fade. As usual with GSM phones, this phenomenon is even more dramatic for the other party, so if the person on the other end complains that you're breaking up, check your hand position.
Neither the loudspeaker or the ear-piece are very loud. If either is set below 50%, they will be difficult to hear. The ear-piece was loud enough to hear conversations in most busy environments at just about 50%. The ringer and loudspeaker requires a much higher setting, especially if you're using a ringtone that's not very loud. The ringtones are of varying volume - about half of them are easy to hear and the other half would sound great if they were louder. Sound clarity and volume appears to vary from phone to phone, as the Erics and Rich each reported different experiences. In no case was quality or volume awful, but rather ranged from "good" to just "acceptable".
The iPhone has vibrating alert as well, but it is as soft as the ringer. Fortunately, the two together provide enough of an alert that we haven't missed any calls yet.
It is impossible to have run a full battery test in just 2 days. Eric Z saw his 20% warning after 48 hours of use including checking email every 15 minutes, calling and iPod use. Eric L used the residual charge of the battery out of the box instead of fully charging it and received a 20% warning after about 24 hours with lots of iPod, Wi-Fi and texting use. Rich's experience was in that same range. It appears as though you can go two days between charges if you use the iPhone as your only phone and iPod and still do quite a bit of surfing with it. The battery life is impressive for something with such a huge-bright display. The automatic brightness control seems to do its job in that department.