- A group of Direct Inward Dialing (DID) telephone numbers are designated for Lync Server Enterprise Voice (EV)-enabled users.
- Some of these DID telephone numbers will be unassigned and available for the future use of Lync Server EV-enabled users.
- A Lync user or PSTN user dials one of the unassigned DID telephone numbers.
- Lync Server performs a reverse number lookup (RNL) on the unassigned DID telephone number and detects that the telephone number is not assigned to a Lync Server EV-enabled user. The call is then routed to the VoIP gateway as an outgoing VoIP call.
- The VoIP gateway recognizes the called number as a DID telephone number that was provisioned for the Lync Server VoIP deployment and routes a request for a new call to the Lync Server VoIP deployment.
- The Lync Server VoIP deployment again performs an RNL on the unassigned DID number and sees that the number is not assigned to a Lync Server EV-enabled user. Again, the call is routed to the VoIP gateway as an outgoing call.