A method and apparatus in a group manager of a central service node, for enabling services or media in a communication network. A monitoring unit detects and monitors activities and conditions of communication entities in the network. A context collecting unit collects individual context data relating to a plurality of monitored entities in order to survey the current situation of each respective entity. A group defining unit then defines a group of correlated entities that are found to be correlated or similar with respect to at least some feature or characteristics based on the collected individual context data, by selecting context parameters of relevance to the group and using one or more membership conditions determined for the group. If the monitored entities have changed their status in a predetermined way that affects the group, the group defining unit will update the group.