Two of the major developments reshaping the telecommunications landscape are mobile wireless connectivity and the migration of voice telephone services to IP technology. These two ideas come together in networks that carry voice services over a wireless LAN (VoWLAN). The importance of usage of VoIP over wireless networks has been increasing, and a lot of research has been conducted to improve QoS and increase the capacity for VoIP traffic. In this paper, we investigate and study the performance of the VoWLAN network, by experimental approach using different scenarios with different codecs. We show that the quality drops significantly starting at 50 simultaneous calls, for the G729 codec. To be close to the reality, we performed the measurement with background traffic.