We had the same problem with Wingo, and bought the other Gigaset Box ( Gigaset Box 100 (DE version) ).
Connected it to the Wingo box and connected the Swisscom phones to it, and it worked. We don't have the Swisscom Davos, but the Swisscom Nyon. But since both work via DECT, it shouldn't be a problem. The only disadvantage is that the management of the DECT phones (names, internal number, etc.) no longer works.