So my Iphone stopped working after less than a year. It was refusing to charge.
I took it in to a "Genius," who said that there was corrosion in the sync/charger port. That, she said, signified moisture, which voids Apple's warranty. Apple even builds a moisture detector into the port, and also inside the phone itself. She opened the phone and found that the moisture detector inside had remained dry, and so decided to believe me that I'd never immersed it in water, and treat it as warranty service. Which is a good thing, because non-warranty service really means that they swap out your phone and charge you $199 for it, and if it came to that I was gonna switch to a different phone.
The bottom line though is that it seems like that port is extremely vulnerable. The rest of the phone was fine even after months of sleeveless use. I am wondering if there is a cap you can get that goes in that port when not in use to protect it.