We have a Trixbox server set up using an SIP connection and I am trying to set up the phones so that users can dial *72, enter their extension, and then forward the number to their cellphone. They want to be able to do this on the fly for any external number. I have confirmed that multiple lines can be dialed out from one extension, but whenever I set call forwarding to dial to an external line and then call in, the phone I am calling in on rings once and then disconnects. I have tried adding 9, removing 9, etc. How do I get call forwarding working without setting up a separate extension for each external number?