I just received my iphone last friday from apple and have been dealing with the proximity sensor issue from day one. I have been debating whether to take it back for an exchange or wait for a patch. My main issue was if I take it into the store I would have a tough time replicating the issue, but I seem to have nailed it down. If I hold it up to my ear and slowly move the phone around it seems to hit a certain spot that the sensor doesn't pick up. Its still a bit finicky to duplicate, but its the only thing I have found. Has anyone else found a better way to duplicate the issue? More importantly those with this issue, have you gotten an exchange that works?