One of the points which, yes, I agree with, but I mainly responded to this:
> I can add phone numbers by enumeration into my contacts and Signal will show who among my contacts is on it.\
> I am not sure about the situation in the US, but in Europe almost all phone numbers are directly linked to a certain person and address by the provider.
Or you can go to a corner shop and buy a Lyca or Lebara SIM with cash. No need to give them your address. You can buy top ups in cash as well. At least in Western Europe this is available everywhere, pretty much.
(I'd still prefer if Signal didn't require phone number to sign up though.)
This is not legal in Norway.
[1] https://privacyinternational.org/long-read/3018/timeline-sim...
Off the top of my head, I think it was easier in France (although this was 16 years ago), Iceland, UK. I also recall it being easy in Aus/NZ. Fairly easy in the US as well, I believe, but as I'm a resident, I don't think too much about what address to use when having a prepaid SIM shipped to me, nor do I ever expect to have to show my papers for something like this. (although, of course, a postpaid account usually involves a credit inquiry, so ID docs would be used privately, not for government reasons, for what that's worth).
Which is still a stable identifier that other people know you by, so you will likely keep it a long time and amass a trail of location data. Also its trivial to tie to the IMEI, so if you actually want to change nyms you have to buy a new phone as well.
Everything about the legacy phone system is a liability. Contact discovery is difficult, but tying into phone numbers should be optional and only for the duration of setting up a contact. Using phone numbers for long-lived identifiers is insane.