Push-to-talk wireless telecommunications system utilizing a voice-over-IP network

A method for push-to-talk (PTT) private calls for users in a wireless communications network, the method comprising:

• joining a user to a multicast group via the wireless communications network, the multicast group having a calling party further joined to the multicast group;
• receiving an SIP request code indicating an invitation to join a private call made by the calling party;
• detecting an acceptance by the user of the invitation to join the private call;
• transmitting an SIP response code configured to join the user to the private call and to remove the user and the calling party from the multicast group;
• and
• receiving speech packets sent from the calling party to the user in a half-duplex manner, wherein at least one of the joining, the receiving of the SIP request code, the detecting, the transmitting, and the receiving of the speech packets is performed by a mobile device.

A method for push-to-talk (PTT) private calls for users in a wireless communications network, the method comprising:

• joining a calling party to a multicast group, the multicast group having a called party joined to the multicast group;
• receiving a selection of the called party to join a private call;
• transmitting an SIP request code to a PTT server via a wireless communications network, the SIP request code configured to specify the called party and to remove the calling party and the called party from the multicast group;
• receiving notification of obtaining a speech token corresponding to the private call;
• transmitting speech packets from the calling party to the called party in a half-duplex manner;
• and
• transmitting a command to release the speech token, wherein one of the joining, the receiving of the selection, the transmitting of the SIP request code, the receiving of the notification, the transmitting of the speech packets, and the transmitting of the command is performed by a mobile device.