Assuming the phone has a standard car kit you could use the sony part (mentioned on boards, search the net) that switches sources based on the amp remote line to switch between the car kit and the empeg. Volume leveling might need to be accounted for as well. You'll also need to hook up the cell mute line to the empeg to pause the music. I'm not sure if there is a better way to handle this.

It would be more difficult to use the empeg's aux-in. Conecting it would be trivial, but a kernel patch (don't think this has been written yet) would be need to automatically switch to aux and back when the cell phone mute is triggered. This might be a good patch for someone to code anyhow.

I'm interested to know what other solutions people come up with.

John