1. A method of managing group information in a communication system providing group communication between subscribers of a first administrative subsystem and subscribers of a second administrative subsystem, the method comprising: storing group information of subscribers of a first administrative subsystem in a first server in the first administrative subsystem; storing group information of subscribers of a second administrative subsystem in a second server in the second administrative subsystem; receiving, in the first server, a request concerning a group management action related to group information of a particular user; checking whether the particular user is a user of the first administrative subsystem; sending to the second server, in response to the particular user not being said user of the first administrative subsystem, an inquiry for the group information of the particular user; generating a response to the inquiry in the second server; and performing the action according to the response to the inquiry.