It seems to be new for Deutsche Telekom, because they are using the adress 192.168.0.1

This is indeed a problem quite common across Europe, or at least I've heard of similar things in Italy, Germany, France and Turkey. Not strictly security related, but useful to know if you install firewall for many custtomer and have to support them after installation. A useful thing to do to work around this, is using 10.0.0.0/8 or better yet 172.16.0.0/12 for the private network. Ciao, Rob!