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You are correct, that the configuration will be done in the DIAL PLAN. Under the DIAL PLAN the NETWORK TERM and USER TERM is designed for what the ATLAS is connecting to. So the NETWORK TERM means we are terminating to the network - which puts the ATLAS in the "user role." The USER TERM means we are terminating to user equipment - which means the ATLAS is in the "network role."
So when you configure a PRI under the USER TERM, then the ATLAS is in the network role, terminating to equipment in the user role. From what you describe, I believe most (if not all) of your PRIs will be configured under the USER TERM. The IN#ACCEPT defines what numbers or number patterns are accepted to be transmitted out the specific PRI interface.
Hope this helps,