Definition:
Numbering Plan Area. A numbering plan allows phone subscribers to make and receive long distance phone calls.
Telephone numbering plans assign area codes to exchanges, allowing dialers to contact telephones outside their local
exchange.
NPA/NXX:
Number Plan Area/Prefix. The area code and the first three digits of a local seven‐digit phone number. This number
identifies the central office out of which the phone number originates.