The following is a listing of numbering terms and their meanings.
| Numbering Plan | A plan for allocation of a unique National Number to each subscriber connected to the national telephone system. |
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| Numbering Area | A part of the country to which a Trunk Code (or area code) has been allocated, and within that area only the Directory Numbers are dialed. |
| Trunk Prefix | The code “0” has been allotted as the Trunk Prefix for automatic national dialing. Trunk Prefix is defined as the digit or a combination of digits to be dialed by a calling subscriber so as to obtain access to a trunk code and the numbering area. |
| Trunk Code | A digit or a combination of two digits identifying the called Numbering Area within the country. e.g. “82 " for Aba numbering Area “1 " for Lagos Numbering Area The prefix “0 ” is not part of this code. |
| Directory Number | It is the subscriber’s telephone number, which is to be dialed to reach a subscriber in the same Numbering Area. It may consist of 5, 6 or 7 digits. e.g. "2691522" - Ikoyi Hotel, Lagos |
| National Number | Trunk Code and the subscriber telephone number taken together. e.g. "1-2691522" - Ikoyi Hotel, Lagos. The maximum length of the National number is limited to 8 digits for Nigeria (i.e. Trunk Code plus subscriber Number) in the present 11-n numbering plan format. |
| International Prefix | The international code is "009" |
| Country Code | A combination of one or two or three digits for identifying the called country. e.g. Country code for Nigeria is "234" while the Country code for Federal Republic of Germany is "49". |
| International Number | The number to be dialed following the International Prefix to obtain a subscriber in another country. The International number consists of the country code of the required country followed by the National number of the called subscriber, but does not include the Trunk prefix used in the national network of the called subscriber. |
| Exchange Code | It is the first one, two or three digits of the subscribers Telephone number (i.e. the Directory Number) which is made use of for identifying the Telephone Exchange to which the subscriber’s Telephone is connected, e.g. "269" for Ikoyi Telephone Exchange "497 " for Ikeja Telephone Exchange. This code is made use of for routing calls between Exchanges within the same numbering area. |
| Local Exchange | It is the Exchange to which the subscriber lines are connected. |
| Primary Centre | It is the Trunk switching centre of the lowest hierarchy to which Local Exchanges are connected for transmitting of subscriber Trunk Dialing (S.T.D) calls. The charge determination for S.T.D. calls normally takes place in the Primary Centre. |
| Primary Area | It is the area served by a Primary switching centre. It may be co-terminus with a single Numbering Area or may cover several adjoining numbering areas. |
| Secondary Centre | It is the trunk-switching centre of higher hierarchy for transiting of traffic between primary centres. It carries only overflow traffic between Primary centres if direct high usage routes are provided between them. |
| Secondary Area | It is the area served by a Secondary centre. It covers several Primary areas depending on the number of Primary centres connected to that particular Secondary centre. |
| Subscriber Number | The subscriber number is that part of the National (significant) Number which follows the Area code. It identifies the subscriber inside his numbering Area. By adding the Area code, the number becomes unique inside Nigeria and forms the National (significant) Number. The combination of this National (Significant) Number with the Country Code identifies the subscriber unambiguously all over the world. |
| Telephone Number Composition | National Calls - National (Significant) Number
International Calls - International Number
Border Communication There are two possibilities for border communications between the Federal Republic of Nigeria and Niger Republic:
The prefix for calls to Birnin Nkoni and Maradi is the digit "9". It is shown in the Numbering Plan at Area Codes "060 " and "065 ". |