I use the FB 5590 as the basis for the Fritzfon C5.
It works perfectly.

Best regards
Gerd

Hi Hugo, I have a DECT phone (wireless) and a Fritzfon C6 connected to the Fritzbox 5590, plus an ancient Ascom aura, + an HP MFP fax, and everything works, I don't quite understand your question ... are you from Walchwil by any chance, then it could be that we know each other :-)

Hi,
The installation worked for me without any problems.
Two fibre optic adapters are supplied with the FB Fiber, you may have used the wrong one, but your electrician would probably have noticed this.

Otherwise, take a closer look at the configuration page http://192.168.178.1: under 'Diagnostics' and 'Internet/Fibre optic information' you can see whether a connection to the Telekom street DSLAM is being established at all. Sometimes the activation takes a while, especially if they are still digging in the neighbourhood ...
Good luck with your installation,
tunanic

Hello Hupo, I have replaced the Fritzbox here in Spain with the Movistar cucumber, I have also connected 2 DECT Fritzfons with different numbers via Sipgate, 2 international (Switzerland + Germany), everything works perfectly. The status says not online, I think the modem is not working or is configured incorrectly. AVM has good support pages for setting up telephony. LG, francs

Hello Hugo
I also have the Fritz!Box Fibre 5590 and it also works without a modem from Quickline.
Install the Fritz!Box 5590 on the fibre optic connection with the correct adapter (if the fibre connection is correct) Connect the Gigaset base station via DECT according to the description of the Fritz!Box and you're done!
I hope it works for you!
LG Thomas