Iphone is in headphone mode with out headphones?

I just got the Iphone 4 about 2 weeks ago, and today everything was working normally until my mom used the App, Tango, to facetime me, we've used it before and it was fine but today when I answered, I couldn't hear a thing, I thought my volume was down and I turned up the volume but then I saw it said (headphones) while I was turning up the volume. Why does it say headphones when I didn't have any headphones in and I've never plugged in headphones into my phone yet. So now I'm using headphones just so I can make phone calls and hear others when they call me. So what is the problem and how can I fix this? I want the speakers to work again, they work when I use the ringtone setting in the settings app. But nothing else works.