A consistency verification tool performs a consistency check on subscriber data records stored in the cellular telephone system. One such consistency check analyzes subscriber data records in a home location register (HLR) and a billing system to determine the presence of duplicate records. Duplicate records can be stored in a duplicate record file for later analysis. During the duplicate record consistency analysis, the consistency verification tool creates a record list. The record list can be a linked list structure for storing main records and duplicate records in a manner that facilitates identifying families of duplicate records. The consistency verification tool can also perform inter-device consistency checks. For example, the subscriber data stored on the HLR can be compared to the subscriber data stored in the billing system to ensure that the two systems have consistent subscriber data.