In a Cisco Unified Communications Manager design where +E.164 destinations are populated in directory entries, which call routing practice is critical to prevent unnecessary toll charges caused by…

Forced on-net routing is critical to ensure that calls between internal extensions, even when dialed with full +E.164 numbers, are preferentially routed within the enterprise's private network. This prevents them from being unintentionally sent to the PSTN, thereby avoiding unnecessary toll charges.

Automated alternate routing (AAR) is used to reroute calls over the PSTN if insufficient bandwidth is available on the IP network, which could lead to PSTN usage.

Forced authorization codes are used to restrict access to certain calling privileges or features, not to prevent internal calls from routing externally.

Client matter codes (CMCs) are used for billing or cost allocation purposes, not for preventing external routing.

Tail-end hop-off (TEHO) routes long-distance calls via the corporate network to a gateway close to the destination, using local PSTN at the destination, which could incur PSTN charges.