NPA-NXX filter enables customers to select the DID number based on North American Numbering Plan (NANP) for North America and Caribbean countries.
NANP telephone numbers are broken down to:
NPA - identifies the first 3 digits as the Numbering Plan Area (area code).
NXX - identifies the next 3 digits in a phone number commonly known as the Exchange.
XXXX - identifies the last 4 digits in a phone number.