Had this same problem. First neither camera worked, then the front camera started working but the rear camera still refused to work. Google said all the usual; restart (no effect) -> hard boot (no effect) -> update iOS (no effect). Apple retailer said it would probably be hardware, and they would replace camera at who knows what cost. VZW warranty services offered to start insurance claim, and would issue a refurbished phone. No thanks. Apple warranty tried FOREVER to get diagnostics, but to no avail, phone wouldn't send info. Offered to have me send it in and get replaced. No time for that. Eventually, a full backup to my macbook -> reset to factory settings -> MAGIC! Camera worked. Hmm... -> restore from backup and voila, all data restored, and the camera works. What a hassle.