Abstract: An exploitation of the proper classification of conventional call processing states into categories, each category corresponding to one of the call states of the SIP finite-state machine (FSM), yields simplified design, implementation, and operation of heterogeneous call processing. A separate FSM for the SIP-categorized call states running in parallel with a conventional port event processing (PEP) FSM, implements a VoIP Local Call Controller by passing events between the SIP-type FSM and the PEP FSM only at the points where a transition between SIP categories occurs. The SIP FSM does not require notification of PEP FSM transitions not affecting the SIP call state. For this reason, none of the code associated with the transitions between PEP FSM states within the same major state category requires any modification. Consequently the integration of VoIP and PEP call processing can be done more simply, and at dramatically-reduced cost in software development, support, and maintenance.