The PBX automatically distinguishes between internal and external numbers with the analysis of the digit sequence and the adjustment of the dialled phone number and the internal dial plan. Therefore, dialling an exchange line access number is not necessary for external phone numbers.

Is required to request an external line. The exchange line access number is only effective when the automatic exchange line request is disabled. Changing the preset 0 results in a limitation of the dial plan and is only meaningful if another exchange line access number is normally used (e.g. in England).