Voice over Internet Protocol (VoIP) service is growing very fast. Service providers offer VoIP service along with traditional data services using the same IP infrastructure. That is why today it is one of the most dominant technologies for communication. In this paper, simulative investigations have been done for VoIP service in WiFi campus network.Step by step, increasing the number of calls, investigations have been done in terms of important Quality of Service parameters like jitter, packet end-to-end delay, wireless LAN load and wireless LAN throughput.