The NALENND™ database is built using GIS data layers to accurately determine service area by Zip Code and accurately maps United States telephone area codes and exchanges to 5-digit ZIP Codes.
NPA NXX numbering resources are assigned by Rate Centers. Rate Centers are the regulated geographic service areas that telecom carriers provide service to and because their boundaries are relatively stable it is possible to compare them to USPS postal carrier routes to determine what NPA NXX combinations are used in specific Zip Codes.
Produced: on or before 5th calendar day monthly
Current Release: March 4, 2018
Distribution Frequency: monthly or quarterly (issue date: January, April, July, October)
Distribution Format: Internet download