Check the following configuration settings:

 

•Minimum length of phone number indication an external call - this is the main configuration setting to determine if a call is internal or external

•Activate the Desktop Notification window for incoming calls to get each call signaled

•The configuration option: Don't show internal calls must be unchecked

•If the internal number is e.g. signaled with 12 but the number stored in the database is  07342/7383-12, see in Prefix for Internal Numbers how to add the company number and area code