Communication via IP can enable the interconnection between many different kinds of communication devices such as cell-phones, 2-way radio, PSTN, Internet phones, VoIP phones, etc. The important key of operating the radio communication or radio-phone hybrid communication is the Voice Operated eXchange (VOX) design by applying an auto-answer mode that supports the accurately enable and disable the voice transmission. In this paper, we present a control algorithm to form a high quality of VOX/PTT operation.