I have an odd problem I can't explain. A couple of times now, I've pulled my phone out of my pocket to find it completely dead. It won't turn on at all. I plug it in to charge and rather than getting the battery charging indicator, nothing happens. Resetting the phone by holding the Sleep, Home, or Sleep+Home buttons does not help.
After letting it sit for about 12 hours, I plug it in again to get the "battery completely dead" sign. There's a red line on the battery indicator, a lightning bolt, and it takes several hours to charge back up.
This has happened to me twice in about the past 6 weeks. I'm wondering if this is familiar to anyone else, because I have 3 weeks left on the warranty and am afraid it will die for good in 3 weeks + 1 day.
Happened to my girlfriend. Somtimes it would sit a day and not charge. Then it would finally power on and report a full charge but wouldn't register that it was charging. Apple replaced the phone and no more trouble ever again. Go before your warranty is up but back your phone up first. Sounds like you need a replacement too.