A system for providing advanced voice services in a wireless communications network (124, 126), the system comprising: one or more servers that interface to the wireless communications network (124, 126) to perform advanced voice services for a plurality of mobile units therein, wherein the advanced voice services include an instant two-way half-duplex voice call within a group of the plurality of mobile units comprising a Push-to-Talk, PTT, call session; wherein both a first server of the one or more servers and the plurality of mobile units that use the advanced voice services communicate with each other using control messages transmitted across bearers in the wireless communications network, and at least one of the servers transmits media streams comprised of voice messages for the communications services between the mobile units across the bearers in the wireless communications network; wherein the PTT call session is initially set up on a default bearer; wherein the first server sets up a dynamic dedicated bearer, a dynamic dedicated bearer being a dedicated bearer that is set up at PTT call setup, in the wireless communications network with a first mobile unit of the plurality of the mobile units, and the dynamic dedicated bearer has a specified quality of service, QoS, for transmission of at least the media streams to the first mobile unit; wherein the dynamic dedicated bearer is setup in parallel with setup of the PTT call session, wherein session initiation protocol, SIP, signaling for the control messages is performed over a static dedicated bearer, a static dedicated bearer being a dedicated bearer that is subscription-based and is established when a mobile unit attaches to the wireless communications network (124, 126), wherein a priority of the dynamic dedicated bearer is based on user roles and a type of PTT call session; wherein the media stream is transmitted on the default bearer until the dynamic dedicated bearer is set up; and wherein the media stream is transmitted on the dynamic dedicated bearer once the dynamic dedicated bearer is set up. one or more servers that interface to the wireless communications network (124, 126) to perform advanced voice services for a plurality of mobile units therein, wherein the advanced voice services include an instant two-way half-duplex voice call within a group of the plurality of mobile units comprising a Push-to-Talk, PTT, call session; wherein both a first server of the one or more servers and the plurality of mobile units that use the advanced voice services communicate with each other using control messages transmitted across bearers in the wireless communications network, and at least one of the servers transmits media streams comprised of voice messages for the communications services between the mobile units across the bearers in the wireless communications network; wherein the PTT call session is initially set up on a default bearer; wherein the first server sets up a dynamic dedicated bearer, a dynamic dedicated bearer being a dedicated bearer that is set up at PTT call setup, in the wireless communications network with a first mobile unit of the plurality of the mobile units, and the dynamic dedicated bearer has a specified quality of service, QoS, for transmission of at least the media streams to the first mobile unit; wherein the dynamic dedicated bearer is setup in parallel with setup of the PTT call session, wherein session initiation protocol, SIP, signaling for the control messages is performed over a static dedicated bearer, a static dedicated bearer being a dedicated bearer that is subscription-based and is established when a mobile unit attaches to the wireless communications network (124, 126), wherein a priority of the dynamic dedicated bearer is based on user roles and a type of PTT call session; wherein the media stream is transmitted on the default bearer until the dynamic dedicated bearer is set up; and wherein the media stream is transmitted on the dynamic dedicated bearer once the dynamic dedicated bearer is set up.