The iPhone 4's second major problem isn't getting nearly as much attention as the first, but it's arguably just as bad -- because it causes you to drop calls. The only difference is that your face is to blame, not AT&T's craptastic network.
The proximity sensor in the iPhone 4 is what tells it how close the phone is to your face so that it can turn the touchscreen off while you're making a phone call. This has the effect of a) saving battery power, and b) preventing inadvertent touches of the screen by your face.
The problem is that the proximity sensor in the iPhone 4 is on a hair trigger. It's either not sensitive enough, miscalibrated or both. In over three years of using the iPhone 2G, 3G and 3GS I've never accidentally hung up on, muted or put a call on speakerphone while holding it up to my face -- not once. Yet I've done it a half dozen times on my iPhone 4 over the past weekend.
As I first blogged about in my iLemon post, I frequently put calls on speaker, or accidentally "FaceTime them" or completely hang up on calls altogether because the proximity sensor errantly wakes the screen, which some part of my cheek proceeds to touch.
And I'm not the only one. There are 66 pages of proximity sensor complaints in this one thread alone (which already has over 100,000 views) from iPhone 4 users in Apple's own support forums.
What bothers me is that the prox bug -- which seems to be more related to software than hardware -- seems like childsplay compared to the antennae/reception issue. Also, it only affects the i4 and so a fix wouldn't have to be QA'd for Apple's other iPhone handsets.
Can't Apple just dial back the sensitivity on the proximity sensor a couple of notches and release a software update? Why is Apple waiting for a "few weeks" and rolling everything into one massive update when it could probably release a proximity fixes for afflicted iPhone 4 users right now? It seems like a comparatively trivial bug and Apple is making its iPhone 4 customers suffer needlessly in the mean time.
Does your iPhone 4 proximity sensor act up?
Update: Anthony Kinson has posted a video of the bug in action. Pay attention to the erratic behavior of the proximity sensor beginning at around the 1:34 mark.
Update 2: Another video demonstration is here.
Update 3: A PowerPage commenter reports that Apple is deleting prox bug threads on its discussions.apple.com
Update 4: Macworld has reported that some users are having success with resetting some of their iPhone's settings.
Many affected users report that either a Settings reset or a hard reboot fixes their problem. One Apple support thread recommends that users open the Settings app, then go to General -> Reset, and choose "All Settings" at the top (note: this will not erase your apps, media, or other data -- that's what the "Erase All Content and Settings" button just below this option is for. "Reset All Settings" just reverts any Settings preferences you've customized back to their factory defaults). One Twitter follower, Brian Partridge, reported that AppleCare told him to just use Reset -> Reset Network Settings, not all settings, and it worked.