In order to facilitate creation of a community without member-specific registration, one or more sibling identifiers with corresponding units to be distributed to other persons are allocated to a subscriber and the one or more sibling identifiers is associated with the subscriber's identifier. The subscriber may then give a unit to his/her friend and when the friend uses the unit, or more precisely a sibling identifier the unit relates to, the system will recognize that the subscriber and the friend belong to the same community on the basis of the association formed when sibling identifiers were allocated.