| Administrative Numbers - numbers which cannot | | | | but are pending use. |
| be assigned to customers and which perform a | | | | Intermediate Numbers - the numbers which are |
| certain administrative function. They may be Local | | | | opened for availability by other carriers or |
| Routing Numbers, employee/official numbers, test | | | | non-carriers which provide phone service to a |
| numbers, wireless E911 emergency service routing | | | | customer. |
| digits/key (ESRD/ESRK), Temporary Local | | | | NXX Code - a block of 10,000 phone numbers |
| Directory Numbers (TLDN), and soft-dial tone | | | | which is identified by the second set of 3 digits in |
| numbers. They are also the numbers used by | | | | the telephone number. This is also known as a |
| carriers for internal operational functions for | | | | prefix. |
| maintaining service standards as well as internal | | | | Personal Communications Service - officially, this is |
| administrative functions. | | | | recognized as "a set of capabilities that allows |
| Aging Numbers - disconnected numbers which, for | | | | some combination of personal mobility, terminal |
| a certain period of time, are not available to be | | | | mobility, and service profile management. It |
| reassigned to another customer. | | | | enables each personal communications service |
| Area Code - also referred to as a numbering plan | | | | user to participate in a user-defined set of |
| area (NPA), they are a set of three digits. | | | | subscribed services and to initiate and/or receive |
| Area Code Split - an area code type where one | | | | calls on the basis of some combination of a |
| geographical region is subdivided into zones which | | | | personal number, terminal number, and service |
| are each assigned a different area code. | | | | profile across multiple networks at any terminal, |
| Area Code Overlay - a type of change in area | | | | fixed or mobile, irrespective of geographic location. |
| code where one geographical region uses several | | | | Service is limited only by terminal and network |
| area codes. | | | | capabilities and restrictions imposed by the |
| Assigned Numbers - the numbers functioning | | | | personal communications service provider." |
| within the Public Switched Telephone Network and | | | | Prefix - a block of 10,000 phone numbers which |
| which are under contract or tariff with customers | | | | are identified by the second set of 3 digits in the |
| for their use. They may also be telephone | | | | telephone number. This is also known as NXX |
| numbers which are not yet in use by customers, | | | | code. |