Recently, my iPhone was having issues. Specifically, it thought headphones were inserted when they weren't. I first noticed the problem as I was typing and didn't hear that familiar "click" that normally accompanies a key press.I thought I had accidentally toggled the ringer mute button (which I seem to do often), but no, it was set to ring. I inserted some headphones and heard everything - the clicks, music, etc.
I placed a call and tried turning the speaker on and off to no avail. Next, I rebooted the phone. No dice. I connected it to my Mac and performed a sync with iTunes and still, there was no sound.
I reset the phone by holding down the power button and the home button. Still, there was no sound without headphones. At last, I got a can of compressed air and gave a couple of short blasts into the headphone port. That did it! The phone must have been interpreting the junk that had collected in there over the past year as headphones.
A simple solution that, hopefully, will save you some time.
I did some traveling this summer (with two toddlers, so don't be envious). Certain that I'd need to conduct a search or two, I bookmarked my destinations on my iPhone, and you can do the same. Just follow the steps:
When you simultaneously press the sleep/wake button and the volume button during a call on the iPhone, you'll immediately end that call and lock the screen.
There's one aspect of the iPhone that's counter-intuitive - the camera. 
Here's a neat feature that almost works beautifully. If you've received a call from a number you don't recognize, go to "Recents" and touch its blue arrow. A window appears that lists the number as well as the 
