Refer to the exhibit. An engineer is confining class of control for a user in Cisco UCM. Which change will ensure that the user is unable to call 2143?

Changing the line partition only controls what numbers ring on that line and doesn't directly restrict what numbers the user can dial out, as outbound calling is controlled by CSS.

Changing the line CSS to only contain Partition_B might still allow calls to 2143 if Partition_B contains the route pattern for 2143, or if the device CSS still grants access to the relevant partition.

Setting the user's line CSS to <None> would restrict calls only from that specific line's perspective, but the Device CSS could still grant access to partitions that allow calling 2143, as the Device CSS takes precedence for many outbound calling scenarios when combined.

In Cisco UCM, the Device CSS combines with the Line CSS to determine the complete calling privileges of a phone. By setting the Device CSS to <None>, the phone will lose access to any partitions defined in that CSS. If 2143 is reachable only through a partition previously granted by the Device CSS, setting it to <None> will effectively block the call.