Landline telephony in new buildings - what options are available?

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Actually, I wanted to use the Fritzbox as a router and for DECT, and an Unifi access point on the upper floor.

Now the question: Can I basically use the Speedport as a slave, only for forwarding to the Fritzbox, and work only with the Fritzbox?
I'm afraid otherwise it will be too much manufacturer confusion.
Or what options do I have?

Regards
KingJulien

Yes ;)
As far as I know, the Speedport uses only the wired DSL part for telephony in hybrid connections anyway. But also regardless: The Fritzbox simply connects to the Speedport (which establishes the internet connection). You can then also register phone numbers (only) in the Fritzbox and implement it as excellently described above by . With that, you could even create a guest network that cannot access your internal network (in addition to / besides the AVM guest WLAN).

But then you have three manufacturers on board: Telekom, AVM, and Ubiquiti with UniFi. How do you intend to operate the WLAN access point (UniFi Controller)?

How do you plan to operate the WLAN access point (UniFi Controller)?

How should I plan to operate it? :D

How am I supposed to run it? :D

The controller does not have to run permanently. Configuring it initially via a PC or Mac is sufficient.

If you want to keep it running all the time, you can either purchase a corresponding Unifi product (Cloudkey, Dream Machine Pro) or run the controller in a Docker container on a server in the network. I do the latter with a Synology NAS as well.

Oh, now it's getting quite complicated again. Are there significant disadvantages to not keeping the controller running all the time? In other words, can you just set it up on the PC and then it runs? In the medium term, I want to set up a NAS anyway. Also, I'm still considering whether to log the heating via the ISG from Stiebel Eltron, or if I should tackle it with a Raspberry Pi and FHEM. I could then also use that (Pi or NAS) as a controller? However, that's the advanced part; first, I have to take care of the basics. Although I think the WLAN in the upper floor would initially be sufficient for us with the Fritzbox in the ground floor, we're not spoiled there, plus wooden beam ceiling. In case I just can't manage it :p