I don't understand. My old one (Gigaset A400) is defective. I need a good replacement for it. What do you suggest?
Thank you Urs

Yes, the Gigaset E290 Duo can be operated via a router with DECT function. If your router does not have DECT, you must use the base station supplied and connect it to the landline.
Here is an alternative: Gigaset C575 A Duo (DE version)