V710 Stuck In Headset Mode

My Verizon V710 (about 3 weeks old), seems to be stuck in "headset mode."

Works fine with plug-in headset, but when headset is unplugged, no sound
comes through the phone's regular earpiece, and the party on the other end
cannot hear me through the phone's mic.

I tried turning the phone off and on, and removing and reinstalling the
battery.

Any suggestions?

Has this been a problematic phone?

Thanks!
Marc