Originally Posted by AmazingApple
How many iPhone 4's will it take, before I can get one that does work, is my question. Mine has been returned twice and I'm on iPhone 4 number three. All three will drop a call when picked up with two fingers anywhere on the sides.
This seems to be a common thread amongst people who experience the problem... which implies that it is not
the specific phone that is at issue. Instead it would seem to be a function of the user
(which is not
to say it is some kind of user "error"). Between how you hold it with your hand, how you hold it next to your face, where you are, what the signal strength is, what the network load is, how much you are sweating, etc. the factors seem to add up to some people have issues and many don't. Some even say that bumpers don't solve the problem, which makes me suspect that they are actually having the proximity sensor issue, not a signal issue. If this theory is correct, it would explain how the phone could get through Apple's testing without raising any issues.
So rather than just getting a new phone repeatedly, try doing something different. Get a bumper. Hold different. Try calls on the headphones. Doing the same thing over and over is likely to generate the same result, at least until Apple changes the design in some way.