As it looks, there is no legally defined router freedom in Austria as of autumn 2023, unlike in Germany, for example.
You have to ask your provider whether it accepts customer boxes and whether it provides the necessary information for configuration and, in some cases, access data (e.g. SIP access data). The situation is similar in Switzerland, where it also depends on your provider.

I have the 5590 in operation with the provider iway.ch, I am also the sole "ruler" of this box, i.e. iway.ch cannot "adjust" anything for me, how it looks in Austria must be clarified with the provider.
Here are the technical specifications of the box:
https://avm.de/produkte...