With the changes from iOS 10, incoming calls are 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.
The telephony function can still only be used with the WLAN at home.

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.