code: public PresenceSubscriber addBuddy(String uri, String eventId, long timeout) {
      return addBuddy(uri, DEFAULT_SUBSCRIBE_DURATION, eventId, timeout);
    }
docs: This method is the same as addBuddy(uri, duration, eventId, timeout) except that the duration
  is defaulted to the default period defined in the event package RFC (3600 seconds).
  
  @param uri the URI (ie, sip:bob@nist.gov) of the buddy to be added to the list.
  @param eventId the event "id" to use in the SUBSCRIBE message, or null for no event "id"
  parameter. See addBuddy(uri, duration, eventId, timeout) javadoc for details on event
  "id" treatment.
  @param timeout The maximum amount of time to wait for a SUBSCRIBE response, in milliseconds.
  Use a value of 0 to wait indefinitely.
  @return PresenceSubscriber object representing the buddy if the operation is successful so far,
  null otherwise.