Reports the number of users connected via the callback service, where the device dials the user back rather than accepting the inbound call directly, for this specific dial-in access code (the table is indexed by the access-code string itself). An admin polls this counter alongside its sibling userStatisticsAccCode* objects to see how the mix of dial-up service types is distributed for this particular acccode (this table's own source DESCRIPTION notes the callback service is not supported on release R100); it lets an admin see how many of each session type are using a particular access code, useful for tracking usage by service plan.