I have a SPA9000 with a SPA400. I have one ITSP phone number and 1 PSTN line attached to Port 1 on the SPA400. I want to be able to route any inbound calls from the PSTN line to a particular extension. It seems to be easy to route ITSP numbers in this way, but I cannot work out how you do this with a PSTN line. Can this be done?