yes, it works, even flawlessly ;)

just needs to be set up correctly, so:
there are several things to consider, speaking from experience, all options work

1. possibility
- connect
- log in
- it works

2. possibility
- connect
- log in
- internet
- access data
- internet provider sunrise
- access type sunrise fibre l3
- now running

3rd possibility (if the way 1. & 2. does not work)
- disconnect pc/laptop from the network
- connect fritzbox to pc via lan
- log in
- system
- backup
- factory settings
- load factory settings
- disconnect fritzbox from pc
- connect
- do 1st or 2nd option
- be happy

Hi PCforever... my "favourite topic"!
I bought the Fritzbox 5590 for exactly this reason, but I was a bit unlucky with the support. But after 4 months I tried again with the Sunrise support... and now it finally works! :)

My requirements:
- Sunrise glass connection via Swisscom, but this will probably be the case almost everywhere, as Swisscom is clearly ahead with the 'last mile'
- I had to give the MAC address of the 5590 to support
- You will receive a 6-digit activation code from Sunrise and then log on to the Swisscom activation page.
- The activation can fail within the first 12 hours after changing the MAC address, which was also the case for me.
- The morning after the MAC changeover, the registration worked

Oh, and one more thing: Yes, even a DECT Fritzfon can be registered afterwards via SIP with the help of Sunrise Support!