Inbound Route Failover

Hi everybody

I have a question about a failover scenario and I’m wondering if it can be done in freepbx at the GUI level or if I’m simply not understanding concepts here.

I have a setup that routes PSTN calls through asterisk to lync using a normal inbound route, destination “trunk”.

I want these inbound route(s) to fall back to ring a set of “emergency phones” which are directly connected to the asterisk server if the lync system should go down.

Any ideas on how that might be possible to configure?