The proximity sensor on my iPhone 4 has been driving me CRAZY and I've been holding the phone to my left ear the same way as I've held every iPhone before with no problems. Which has been like this... I thought...what would happen if I moved it up a bit so the sensor was at the top part of my ear instead of at the hole part of the ear. So far, in the 3 calls I've made, it seems to have fixed it. Will have to see some more of the next couple days and it does require you to think and focus on how you are holding it but at least I can use the phone.