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 geographic location of a mobile device, such as a mobile telephone associated with the user system, may be disseminated to users on the participant list or people on the contact list based on geographical location information that is associated with groups of users or contacts. A user interface enables a user to specify the manner of disseminating on-line presence information and/or geographic location information to groups of users or contacts. 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 top people on the contact list base on notification information that is associated with groups of users or contacts. A delegation model may be used to control whether a user is permitted to make modifications to the notification information. The user may use multiple identities to communicate within the instant messaging system and/or with the mobile communications device or devices. The user can maintain sets of temporal periods for each of the multiple identities. Only one identity may be used at a specific time to communicate to a specific other identity, but the multiple identities of the user may be linked such that on-line presence and/or geographic location associated with one of the identities is disseminated based on the temporal periods set for one or more of the multiple identities. |