iPhone 4S Sound Problems

My phone no longer outputs any sound via it's speakers. I can hear sound with headphones and also if it is connected by the dock connector it will output sound to whatever it is connected to.

I have tried plugging and unplugging headphones several times thinking that it is stuck in headphone mode but that did not resolve the problem. I tried a factory reset in case it was software related but that didn't fix it either. I am out of ideas at this point. The phone is four months out of warranty so I'm not sure genius bar will be much help.

Any ideas would be appreciated. Thanks.