A 3-digit code in the (NPA) numbering plan area (N) format, which are used as the first three digits of a 10-digit address in a North American Numbering Plan dialing sequence. Although NPA codes are normally used to the purpose of identifying specific geographical areas, certain of these NPA codes have been allocated to identify generic services or to provide access capability, and these are known as service access codes (SACs. ) The common trait, which is in contrast to an NPA code, is that SACs are nongeographic. One of the key requirements associated with an address containing a SAC is the ability to discern the appropriate carrier. To satisfy this requirement and to alleviate confusion, the term SAC is subdivided into categories that characterize their carrier identification requirements. The 3 subdivisions are ancillary carrier identification, embodied carrier identification, and external carrier identification.