Number of RJ-45 sockets "network sockets" - What makes sense?

Sorry everyone - I didn't mean to start a wild discussion. What I mainly meant was: When I get the SIP credentials (username and password for the "telephone" connection) from my provider, I only have to think about RJ45 network cabling/Wi-Fi coverage and no longer about additional telephone wiring. I simply have the option to connect suitable devices wherever there is internet. This pays off in my case in the garden, the basement, and at the neighbor’s (who happens to be my parents). If I wanted, I could set up a phone at my girlfriend's place - only my wife would be against it. And that is exactly an advantage compared to the past when people still had to deal with splitters/ISDN systems/analog phones. Since I imagine not every builder is aware of what is possible today, I made the remark.

If I get the SIP credentials (username and password for the "telephone" connection) from my provider, [...] I could set up a phone at my girlfriend's place

Correct
Theoretically, you can make your iPhone use your landline number to make calls from your furthest garden corner where the neighbor's Wi-Fi is already closer than yours - and you are certainly right that the average homeowner probably hasn't thought of this yet

I still have 5 devices.