In general, the internal numbers are the user's numbers on which he can be called internally, i.e. by other users at the same location or from other networked locations. In earlier versions, this was implemented with the extension, i.e. a part of the user's external number. (Example: External number +49 231 5666 227 -> Internal number 227). From Version 6.x it is now possible to assign the user an individual internal number. This internal number is freely definable and need not necessarily correspond to the extension of the external number, though this is the most common way of assigning internal numbers. (Example of an internal number that differs from the user's extension: External number +49 231 5666 227 -> Internal number 5227). This internal number can consist of any number of digits up to a maximum of 10 digits. It should merely be ensured that the format of the internal numbers does not conflict with other numbers or codes used in the system. For example, an internal number cannot begin with "0" if this is defined for the public line access for this location. It is also possible for a user to be assigned more than one internal number. It is not permissible for a user's internal number to begin with another user's internal number. Example: User1 has the internal number 12345, User2 may not be given the internal number 1234, but 1235 is permitted.

The introduction of internal numbers enables a common number plan to be used in networked SwyxWare locations.

This approach will be briefly illuminated in the following example: A company at a Berlin location gives all employees a three-digit internal number beginning with "2" (e.g. 201, 202, 203...). The internal numbers of the company's networked SwyxWare location in London begin with "3" (e.g. 301, 302, 303, ...). When the numbers are assigned in this way and the forwarding tables are configured accordingly, it is possible for all employees to reach all other employees, even in other locations, using the internal numbers.