A user of an instant messaging system may store names of other users of the instant messaging system on a participant list (which may be referred to as a "buddy list"), and the names may be categorized into one or more groups. Similarly, a user of a mobile device, such as a mobile telephone, may store contact information about people on the mobile device. Information describing the on-line presence of the user within the instant messaging system or the geographic location of a mobile device, such as a mobile telephone associated with the user, may be disseminated to users on the participant list or to people on the contact list based on notification information that is associated with groups of users or contacts.