The tremendous advances in the field of multi-service networking have enabled the integration of voice and data networks leading to a reduction in the overall network setup and maintenance costs. In this paper, an evaluation of Voice over IP (VoIP) and Voice over ATM (VoATM) with respect to delay and link efficiency is presented. OPNET Modeler 7.0 was employed to simulate the network scenarios for comparing the performance of VoIP and VoATM technologies using different coding schemes. Simulations show that the major factors affecting the performance of a consolidated voice and data network are QoS parameters and coding schemes. VoIP was found to deliver better performance compared to VoATM for a lower voice call density, while VoATM was found to be more robust at higher call volumes