Plug and unplug the factory set of headphones that came with the phone a couple of times really slowly. It's a known bug that sometimes happens on select handsets. The phone thinks it's in headset mode (i.e. headphones).
If headset mode is active though, on the call screen, wouldn't you be able to see the image of the headphones next to the phone handset picture on the left side of the screen.
Have you checked to see what the image status shows while on a call? I agree... the headphone jack trick works more often than not, thats for sure.
Civic - off subject and sorry to thread jack - your tag, is that image of you? lol... just been curious for a while, no reason really.
For me, plugging in headphones, doing a battery pull, and turning it back on with the headphones in and then taking them out after it had fully booted back up fixed it.
