Solnet support writes back helpfully on 29.06.2023 when asked and explains on the phone: If the owner opens a temporary remote access for Solnet, then support will help by phone to set up internet AND TELEPHONE.

E-mail dated 28.06.2023: The Fritz!Box 5590 is not officially certified for Switzerland. SolNet connections have no hardware restrictions. You can use any hardware you like. However, please note that with such connections only basic support (connectivity) is guaranteed and the customer is responsible for the configuration. With your own Fritz!Box, telephony is also not possible, because the phone number is permanently stored on the Fritz!Box by SolNet and access data is not made available to the customer.

i have the fritzbox via sunrise running, @FranzB456 did not have to change away from that, because the fritzbox supports all providers, if not abwerk then halt manual, let the provider give you the necessary data, have fun with the fritzbox, have everything from fritz, runs everything super best's, never again something else!!!!

provider experiences with fritzbox:
- sunrise
- bluewin
- upc cablecom
- iway
everything works perfectly

@Mailinglist hope I could answer your question

Hello I put the Fritz!Box5590 with IWAY.CH into operation -> it worked great. Had to switch from Sunrise to IWAY. Sunrise was not prepared to support the Fritz!Box5590. Very bad reputation for me.

Hello, I have the Fritz!Box5590 with Wingo in operation. It works perfectly.
However, I had to call support so that they could make a few more settings.
settings. That took a few minutes. Since then everything has been tip-top.
Hope that helps you