Teletraffic engineers provide models allowing communications networks to be planned and systems to be designed to meet the performance needs of users within a reasonable cost. The successful modeler combines analytical or simulation skills with a deep understanding of the technology. In the emerging information networking environment comprising new technologies such as ATM, Internet, wireless, etc., and new services such as video, multimedia, data and personal communications services, the old paradigms of circuit-switched calls and Erlang distributions have been severely challenged. The confluence of the shifts in technologies and services along with the convergence of computing, telecommunications, consumer electronics, and electronic media industries, and the shift from a monopolistic to competitive business paradigm, has created a tremendously rich lode of fundamental problems that need to be addressed by teletraffic engineers. In this article the author describes the historical role of the teletraffic engineer, reviews several of the major paradigm shifts, and discusses some of the challenges facing the teletraffic community with an emphasis on modeling wireless communications systems.