Abstract: Billing records for call attempts directed to an inbound subscriber are sorted by originating telephone number, date and time of day in order to group together a) sequences of call attempts initiated at each telephone number, and b) corresponding disposition for each call attempt in that sequence. When the billing records indicate that all call attempts initiated from an originating telephone number have been unavailing (blocked calls, ring-no-answer), a caller associated with that telephone number is deemed "lost" with respect to a selected time window. The number of lost callers within a predetermined period of time is then used to determine the desirability of committing additional resources to a call center.