when a voice call is made between two users , both of which may have access to multiple voice communication services , the connection is made automatically by the communication equipment through a selectable communication service , based upon characteristics of connection . those characteristics may include the services available to the users , the day of the week , the time of day , the availability of the callee on a service , the geographic locations of the caller and callee , and caller pre - established service preferences . preferably , caller preferences and associations of callees with unique destination identifiers are stored in a database created for the caller and available to his communication equipment . an ultimate callee identifier selected for a particular call includes an indication of communication service , and connection an appropriate interface for that service is then provided automatically for the caller .