This is my first iPhone and overall I'm really enjoying it. Though yesterday my phone went into "headphone mode." I have never used a pair of headphones with it yet. I looked up the problem and tried plugging in headphones a couple of times. Turned Bluetooth on and off a few times. Blew into the headphone jack. Restarted the phone. Backed up the phone and factory reset it. Nothing. I don't see anything in the headphone jack like dust or lint. Any else having this problem? Should I take it to the Apple store?