Voice over IP (VoIP) has become a popular Internet application. Mobile Ad-hoc NETworks (MANETs) may provide a good platform for the fast deployment of VoIP service in many application scenarios. The luck of infrastructure, flexibility and low cost are the main characteristics of MANETs. Otherwise, its present a considerable complexity that makes the transmission of real-time applications like VoIP a great challenge due to Quality of Service (QoS) requirements. This paper investigates the performances of routing protocols (AODV, OLSR) in MANETs carrying VoIP traffic.