Here is a fix that I would like to pass along. My wife's iPhone 4 was dropping just about every call. It wasn't an antenna issue, it was a proximity sensor issue where during a phone call the screen would come back on and she would hang up with her face or go into other menus.
Apple's latest update (4.1) has a proximity sensor adjustment to make it more sensitive so that the screen stays off much better. If you get this issue check your version first through the settings app and update your phone if you are behind. We searched the net and nothing about an update came up so we wasted the entire day in the Apple store for them to tell us to update the phone Hopefully this can help save time for others.
my phone have this problem, I decreased my iphone on a container with water. The property choice is not operating and when i converted off then switched on the product, speech management instantly triggers. I went to DJGT for fix and they changed your property choice. I used my cellphone without any issues then after 1 day, the problem again happens. So i went again to DJGT then they examine my device, fresh some areas with liquor. Again after one or two periods the problem still happens. I went returning again for the third time to DJGT, they changed broken capacitors on my cellphone. But still, it did not fix the problem. They informed me that the problem is in the IC but they have no areas available. Is there any efficient iphone mechanic aside from DJGT?