Thanks for the help guys. I never thought to check the player config, hehe, since I haven't messed with it for a while now. It makes sense, given the incredible configurability of the empeg, that it would let you decide how to trigger the mute.

I played around with the Treo headset yesterday, and I found that the speaker is completely dead while the phone is ringing. It only activates once I press the single button on the microphone pod. The plug that fits into the Treo looks to be a standard 2.5 mm headset jack, but it has 4 (?) connections on the plug. All the other headsets I've seen have 3 conductors: one for headphone, one for mic, and one for ground. I already ordered another headset, and I plan on taking it apart to see if I can somehow trigger the cell mute line automatically when the phone rings. It looks like I'll have to hack together my own hands-free car adapter, or just mount a switch somewhere to make the phone think it's off the hook.