teran, make sure you post back and let us know what it is.

I do not believe it is a stuck button. That's what I originally thought it was too until I tried to simulate it. If the phone has full handsfree enabled, and that button is stuck, the set is on all the time (cannot release). If it's any other button stuck, it's on speakerphone until you pick up the handset (works like a normal phone).