The area code forms part of a station number in the UNKNOWN OpenScape 4000 numbering scheme for open numbering. The area code is the route code dialled to access a specific area. The area codes can correspond to the node number hierarchy level, but do not have to. For example, the node with the node number 1-2-3 may have the node code "99". This is the standard case in single-level networks converted to multi-level networks, if the station numbers are to remain unmodified. The node may also have the 3-level code 11-80-99. In this case, the level 2 area code is 11, the level 1 area code is 80, and the level 0 area code is 99. A station number 4711 within that node must then be dialled as 1180994711 from other nodes in the network.

The area codes are entered under the appropriate network level in the KNMAT AMO (LEVEL=0 or 1 or 2).