Was having proximity sensor issues with my iPhone 4
From day one I've had proximity sensor issues when I'm not using my Motorola H721 Bluetooth earpiece. Went in this morning at 11:00 am with an appointment with the Genius Bar at the local Apple Store (scheduled it last night using the Apple Store app). It took 30 seconds to explain the problem to him. I didn't have to re-create the issue, and he replaced it, and he even gave me a free plug adapter that I had misplaced. I haven't had any proximity issues with the new replacement phone.
I did have Ghost Armor put on my phone over a week ago, which I removed while speaking with the Genius guy before handing it over to him. I'm wondering if the Ghost Armor had anything to do with the proximity sensor issue, or if they have upgraded the sensor in the second shipment... I wish I would have tested my original phone after removing the Ghost Armor. Now I'm not sure I want to put the Ghost Armor back on the front of my replacement iPhone.