Unless you have a Swisscom Internet box, with which the devices also work.

On the AVM page there is an INFO about: Usable functions on base stations from other manufacturers.
Digitec could possibly include this in the product description: http://avm.de/service...

The Fritz telephones transmit according to the DECT standard for cordless telephones. Any modem/router that can also function as a DECT base station can in principle also be connected to the Fritz telephones. However, the Fritz telephones are quite good at supporting the latest standards (encryption!). With a different base station, you may not have the full range of functions. A WLAN router is not enough. As someone else wrote, these things don't use Wi-Fi, they use DECT.

No, they only work with a Fritzbox
The transmission is not via WLAN.