Patent ID: 7620160

Claim:
A computer-readable medium containing instructions for controlling a computer system to provide a ringback tone by a method comprising: subscribing with a presence server to receive presence information of users, the presence information of a user including a mapping of a telephone number to the user; receiving from the presence server notifications of changes to the presence information of the users as the presence server is updated with the presence information of the users and storing the presence information of the users as indicated by the notifications; receiving an indication of an incoming call from a caller to a telephone number; identifying a called user from the called telephone number using the mapping of users to telephone numbers of the stored presence information; retrieving from the stored presence information presence information for the called user identified from the called telephone number, the presence information including availability of the called user; and before the incoming call is answered, outputting to the caller a ringback tone indicating the availability of the called user wherein the ringback tone indicating the availability of the called user is output before the call is answered so that the caller knows the availability of the called user before the call is answered.