I do not know of an easy way to find out what the prox sensor is. Someone would have to take apart the phone and try to identify a part number or etc. I am sure that the majority of the electronics are surface mount components. The IR sensor may not be surface mount, but I bet it is very small. The point being that it could be very difficult to visually identify a part number or etc to track it down.
I repeated my testing and observed the same range and etc. If anything my phone turns off the display at a slightly shorter distance. The problem I do not think is the range of detection of the sensor. I still noticed that the trigger point (distance to turn off the sensor) changes. The distance required to turn off the display gets shorter (memory effect for lack of a better term) as objects (face) get closer. Some people say that it is not sensitive enough. I would argue that it is the opposite. The sensor becomes more sensitive. This seem like a software issue to me. However, it could be electronic as well. I first thought it was software, but since the update did not seem to change it for my phone I am not sure. It could be that Apple just has not fixed the software issue. It could be electronics. Some electronics can be very heat sensitive and etc and create strange results. I still lean toward software as the problem.
The sensor seems to detect an object at appx 1.5" at the start of a call. It changes as the object gets closer (more sensitive). At that point it does not take much movement to reactivate the display. If Apple could set and keep the detection range at the Appx 1.5" range, then it would be ok.
The other problem is the distance it takes (movement away) from the object to reactivate the display. The previous IPhones seem to require the object (face) to move away the entire detection range before the display reactivated. The Iphone 4 takes a much shorter distance to reactivate the display. Again, this makes it more sensitive.
I made some test calls to check it out after the update. I revolted the phone to be safe and fair. I could see the display turning on with very slight movement (over sensitive). I kept the phone placed on my ear and moved it slightly. It remained in contact with my eat the entire time. The display would turn on like before. I faced dialed just like before. If you leave the phone very still don't move it, then it may not act up. To be fair, I did get a call from a co-worker afterwards and the call was fine with no face dialing. I did move the phone from ear to ear some during the call. Remember my previous post about how the sensor resets the detection distance when the object moves past the detection range of about 1.5" to 2". I have found that I have less face dialing if I move the phone away from my face every so often and then place it back. This could explain why people have different experiences. Their call habits are different and this could reset the range every minute or two and the problem is less for them.
If the problem were heat related or etc, then the sensor would most likely start acting up once it reached the temp threshold and keep acting up until it cooled down. This would mean it would act up the entire time it is over heated.
Most companies would design a hybrid software and hardware method for this. This would give them options to fix issues like this andeven use it to add some type of feature or etc. Apple is not stupid and I am sure that they would have thought of this. This is the reason that I think that it could be software.
We may never know unless Apple gives us information. We may never know unless they fix it some way.
