Abstract: A method allows an individual PoC client and a PoC client belonging to a specific PoC group to participate in a session as extended targets while a PoC group talk is proceeding. When the PoC client that is participating in the ad-hoc group talk intends to make the ad-hoc PoC group session ongoing by adding both a plurality of individuals and members of at least one PoC group to the existing session as preliminary talkers, the list information is obtained by identifying the group URI at the PoC server. By using SIP or Extended SIP and XCAP in this process, the PoC user that is participating in the group talk transmits the single SIP message through an ongoing session, and invites a specific PoC group and a plurality of PoC users who are designated voluntarily to the ongoing PoC group talk. Thereby, the PoC user can perform the PoC call.