Question about Comfort 500A Duo - 597751

This is because the telephone can be connected to a UPC router via an RJ11 to RJ45 socket.
Wirewin Câble téléphonique RJ11 à RJ45

As for the difference, the CH version comes with a cable that allows you to connect the phone to a wall socket that complies with Swiss standards (as opposed to the German standards of this non-CH model).