Referring now to FIG. 3, the exemplary call management system 112 is shown in more detail. In exemplary embodiments, the call management system 112 comprises a PBX 302 and router 304. The PBX 302 is configured to provide communications via the PSTN 108, while the router 304 is configured to provide communications (e.g., VoIP) via the IP network 106. In some embodiments, the PBX may comprise an iPBX, which eliminates the need for the router 304. The call management system 112 may further include one or more memory devices 306. The memory device 306 comprises a communication interface module 308, dynamic address engine 310, settings module 312, call routing module 314, fallback module 316, and local relational database 318.

The communication interface module 308 is configured to provide a user interface for configuring and managing functions of the call management system 112. For example, an administrator is able to create VoIP accounts and establish dial plans via the interface provided by the communication interface 306 of the call management system 112.

In exemplary embodiments, the dynamic address engine 310 is configured to handle private addresses. The dynamic address engine 310 may operate to determine and maintain a list of private (internal) addresses associated with each network device 110 coupled to the call management system 112. The dynamic address engine 310 may comprise, at least, an address check module and local lookup module as discussed in U.S. patent application Ser. No. 11/506,279 entitled “Mobile Use of a PBX System,” which is incorporated by reference.