Never mind--I found out how to use it (it's the middle round button with Cingular logo)
I just got an LG c2000 that has a speakerphone function. The booklet tells you to press the [OK] key during a call to activate it. Does anyone know which key this is? I thought it was either the top key in the far-left or far-right corner but all the left one does is mute and unmute, and the right one brings up a menu that has nothing to do with a speakerphone.