We have multiple WEBS towers (made by Talk-A-Phone) bridged to the same line that pick up when you call that extension a device called a ZPS does this. As we have been adding more though the chances of them picking up simultaneously has decreased. My boss is looking at ways to get all towers on the same ZPS unit which would involve audio to fiber conversion to the more remote towers so don’t get carried away looking for this. But have you ever heard of a device that can sense the voltage change when one has picked up and automatically pick up and connect to the speakers and then hang up when the voltage returns to 48 volts? It might need to have a switching function for the amplifier also just so we don't have to leave the amp on all the time. Thanks