Planning for the UM role requires you to consider the following UM-related areas beyond server placement and configuration:
UM Server The server that handles voice access. UM servers can handle calls for multiple dial plans and thus can be associated with multiple UM Servers.
UM Dial Plan Represents a set of telephony-enabled endpoints (extensions), sharing a common numbering or naming plan, defined by the telephone network (such as PBX).
UM Hunt Group A hunt group associates an IP gateway with a dial plan, and may have a pilot number to distinguish gateway associations with different dial plans.
UM Mailbox Represents the UM-enabled user. The mailbox has an extension assigned to it in an associated dial plan. Users can ...