Hi @chrisse , if your carrier is Salt Switzerland, I’d recommend pushing them to escalate your case further up their technical support chain.
I had a very similar experience with my BlackBerry Key2 in the US last year. It’s an older device than the FP4 (Android 12, no 5G). Everything seemed to work when I landed, quickly after, no calls, changing local network would do nothing. After I really insisted to Salt and got the issue escalated (they asked me several times to specify some phone number/time of calling to run their test), they cleared whatever was blocking it, and it worked perfectly again. I didn´t have to do anything on my phone, it was on their end.
In my experience, first- and second-level support often can’t resolve more complex network issues, so it’s definitely worth insisting on an escalation.