Although the iPhone 4’s reception issues get all the press attention, the iPhone 4 has another pressing issue: the tendency of the proximity sensor to misread how close your face is to the handset, which can in turn cause the touchscreen to turn on when it’s close to your face, allowing your chin or cheek the unfortunate liberty of blindly dialing or even hanging up during a call.
The proximity sensor issues are commonly theorized to be a software issue, but according to an Apple Store Genius spoken to by TUAW’s Aron Trimble, we may be looking at another design flaw.
Why? According to the Genius, Apple had to move the proximity sensor location in the iPhone 4 so that it actually points into the ear canal during a call. That means that if you have particularly glistening ear canals, light bouncing around the ear canal can mistakenly tell the proximity sensor that you’re no longer on a call.
The Genius’ recommendation on how to fix the issue? He said that you should make your calls from somewhere darker.

