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In traditional CDMA wireless networks, real-time services, such as circuit-switched voice, are transported over the air via synchronous channels because of their stringent delay requirements. In the third generation networks (3G), IxEV-DV [A.Soong et al., 2003] and HSDPA [E. Dahlman et al., 1998], an additional time shared channel was introduced on the forward link to support data services for which delay requirements are less stringent. The IxEV-DO [P. Bender et al., 2000] standard provides a single time-shared forward link channel and no synchronous channels since it was designed primarily for data services. It has recently been suggested that certain voice services (e.g.. Voice over IP (VoIP) and push-to-talk (PTT)), can be efficiently transported over such time-shared channels since they have less stringent delay requirements compared to circuit-switched voice. In this paper we investigate the capacity of VoIP users over these time-shared channels and investigate the sensitivity to various base station (BS) and mobile station (MS) design parameters, algorithms and features. Note that detailed simulations of each standard is not provided but rather a comparative approach is used whereby we investigate specific features of each standard. Our focus is on the forward channel since code division multiplexing is performed in the reverse link and hence comparable user capacities are achieved.