If you already have a "rabbit-hole" configuration and the new, "fail-over" PRI will present the inbound calls with the same DNIS digits then the only change needed should be to add the new PRI in the DIAL PLAN under the NETWORK TERM. The ATLAS accepts inbound calls on any of the NETWORK TERM entries and then routes them to the USER TERM based on the USER TERM's IN#ACCEPT LIST. So if the DNIS is presented the same (or you are simply using the wild card of "$") then the ATLAS will route the call regardless of which PRI the call comes in on. If the DNIS is presented differently then you can add the "new" DNIS to the IN#ACCEPT LIST in order route the call properly (i.e. if one PRI presents a 4-digit DNIS and the other PRI presents a 7-digit DNIS you can have both versions in the IN#ACCEPT LIST).
Hope this helps,
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