If you have activated "Only use at home" in the telephony settings, incoming calls will be displayed when the telephony function is activated, even though the user is not connected to the WLAN of the Internet box. 

The call screen is displayed briefly and the user receives a message that it is not connected to the WLAN of the Internet Box.
Solution:

Add your address in the "Help" section of the Home App. After that, you should no longer receive the notification when you are away from home.