I have 3 trunks coming into my pbx, I want one to be the main number. I would like to take calls coming into that trunk (trunk 1) and send them to another trunk that is not busy (trunk 2 or 3). Outbound is easily handled by me assigning max channels and and outbound routing order to each. Incoming I want trunk 1 to always be available unless the other two are in use. Any way to accomplish this, has anyone done this with asterisk?