A method in a call information server for a two-way radio system includes accessing, by the server, group list information associating the plurality of subscriber units with one or more groups; receiving, at the server, updates related to presence information, availability information, and the group list information; and confirming, by the server, for each particular subscriber unit indicated in a particular group list as forming a particular group, the particular subscriber unit's participation in a particular group call to the particular group, as a function of the presence information, the availability information, and the group list information. A call information server and a two-way radio system are also disclosed.