I ran into a situation with outbound rules. I have a PSTN line which handles local traffic and a VoIP provider that handles long distance traffic. If my PSTN line is busy, calls forwarded to it just disconnect. Opps. I have extensions set up to dial my mobile number (local number) if my handset is RNA. If my PSTN line is busy, the call is dropped. So there needs to be a way for outbound rules to provide for "overflow", i.e. allow calls to use a second path if the primary is not available. The same would hold true if my VoIP was down and I need to make a LD call.