Lotus Sametime Unified Telephony supports closed and open numbering plans as well as implicit and explicit numbering.
An open numbering plan is a dialing scheme in which the caller must dial the location code plus the extension number. Typically, location dialing includes the dialing of the on-net access code as well. Location dialing plans are also known as location dialing plans or multi-domain networks. In the enterprise environment, private networks typically use location codes to implement an open numbering plan.
A closed numbering plan is one in which the number dialed to reach a given party is always the same, regardless of where in the network the caller is located. In the enterprise environment, the extension dialing plans used within a single switch or in a small private network consisting of several switches are examples of closed numbering plans.
Parent topic: Numbering Plan