A system for providing voice communications services in at least one wireless communications network (124,126), comprising: one or more servers (108, 110, 112, 114, 116, 118, 120, 122) that interface to the wireless communications network to perform communications services for one or more mobile units therein, wherein the communications services include an instant two-way half-duplex voice call within a group of the mobile units comprising a Push-to-Talk PTT call session; wherein both the servers and the mobile units that use the communications services communicate with each other using control messages within the wireless communications network, and at least one of the servers switches voice messages for the communications services between the mobile units across the wireless communications network; wherein a first server of the one or more servers manages the call session by acting as an arbitrator for the call session and by controlling the sending of the control messages and the voice messages to and from the group of the mobile units; and wherein a first mobile unit of the group of the mobile units performs Relay-Mode operations using WiFi communications for delivery of the control messages and the voice messages to and from other mobile units of the group of the mobile units, characterized in that the Relay-Mode operations comprise: receiving, by the first mobile unit, a unicast IP packet encapsulating a multicast IP packet for the PTT call session from the first server over a wide area network WAN; and forwarding, by the first mobile unit, the multicast IP packet to at least one multicast router within a private WiFi network, wherein the multicast router routes the multicast IP packet within the private WiFi network. one or more servers (108, 110, 112, 114, 116, 118, 120, 122) that interface to the wireless communications network to perform communications services for one or more mobile units therein, wherein the communications services include an instant two-way half-duplex voice call within a group of the mobile units comprising a Push-to-Talk PTT call session; wherein both the servers and the mobile units that use the communications services communicate with each other using control messages within the wireless communications network, and at least one of the servers switches voice messages for the communications services between the mobile units across the wireless communications network; wherein a first server of the one or more servers manages the call session by acting as an arbitrator for the call session and by controlling the sending of the control messages and the voice messages to and from the group of the mobile units; and wherein a first mobile unit of the group of the mobile units performs Relay-Mode operations using WiFi communications for delivery of the control messages and the voice messages to and from other mobile units of the group of the mobile units, characterized in that the Relay-Mode operations comprise: receiving, by the first mobile unit, a unicast IP packet encapsulating a multicast IP packet for the PTT call session from the first server over a wide area network WAN; and forwarding, by the first mobile unit, the multicast IP packet to at least one multicast router within a private WiFi network, wherein the multicast router routes the multicast IP packet within the private WiFi network. receiving, by the first mobile unit, a unicast IP packet encapsulating a multicast IP packet for the PTT call session from the first server over a wide area network WAN; and forwarding, by the first mobile unit, the multicast IP packet to at least one multicast router within a private WiFi network, wherein the multicast router routes the multicast IP packet within the private WiFi network.