Lost sound and screen stays on iPhone 4

When trying to use my iphone 4 to listen to a podcast tonight, I got no sound at all. I then tried some music - no luck. Then I tried a call (just calling 611 for the ATT automatic help line) - nothing. I have no idea if anyone would be able to hear me.
Also, and this seems odd, the screen also stayed off during the call.
The only way I can hear anything is with earphones (havent tried bluetooth though).
I tried turning it off and then back on. Tried holding down the top button until the slider appears and then waiting for it to return to the normal screen. Tried the same thing, but holding both buttons down. And tried both buttons and then, when the slider appeared, continuing to hold the home button until things returned to the normal screen.
Nothing works. Set up a genius appointment for Thursday, but hoping to get some help here.
I do have a theory, based on the screen not turning off at all - maybe the phone thinks a headphone is plugged in even when it isnt.
Macbook Mac OS X (10.6.2) http://picturehawaii.blogspot.com/2010_09_01_archive.html