Don't take things like that too seriously. That's just the result of the reality distortion field that comes with sitting on top a huge database of phone numbers.
Simple: usernames. Humans are not phone numbers. Phone numbers are the IP addresses of legacy phone networks.
A lot of countries require require registering the phone number to your name.
Relying on phone numbers as uniqie identifiers especially in "crypto" hipster apps (Signal) is stupid bordering on malicious
If said malicious actors pwn the phone of the person you were talking to, suddenly they have a pretty good way of mapping a contact called "My Best Friend" to a human through billing records.
Or even easier, they type the phone number into Google and find that the Syrian dissident they've just arrested has been corresponding with the NYTimes or BBC.
If they know only that they are talking to [email protected] they could, uh, get Google to release their IP address. Google are fairly unlikely to honour a legal demand for disclosure from Libya or North Korea or some other tyrannical/fucked-up hellhole.
I like Signal, but I'm not totally sure about the threat model.
* They're not portable. My username here is Zak. It is on reddit as well, but I think that's the only other place. If I don't discover a service within it's first week of operation, I won't get that username, and many won't allow it because it's "too short".
* They don't tap into users' existing contact lists. I've discovered several people I know using Signal because I had their phone numbers stored in my phone's contacts.
But if a new communications protocol is to replace the legacy phone network, which I consider desirable, it probably shouldn't use identifiers tied to the legacy phone network.
1) get US phone
2) register google voice to US phone
3) stop paying for US phone
4) you can't de-register you US phone, unless you register a new one
5a) if you never sign up for a US phone, anybody can get assigned that number and click "forgot password" on your google voice.
5b) you get a new US phone: go to 2.
that is true for every single service that ties you up to a phone number or that has phone number as recovery option.
I've also read using Google Voice is highly recommended for things that require a voice or text number since it's very difficult to get hold of someone at Google that can be socially engineered. Much easier to scream at somebody at Verizon, etc.
The cheapest I've seen slightly below $2/month, but all the super cheap carriers are very volatile businesses and you can't expect to keep them more than a few years.
Seeing as you don't really own phone numbers in the sense you own domain names, any permanence is limited by the life span of your service provider.
> addressing with user-owned identifiers like phone numbers
Phone numbers are owned by telecoms, not users. Sometimes they're transferable between telecoms, but not always. I, in particular travel internationally often and do not maintain phone service in the same country continuously. I've had to change phone numbers with Signal and Whatsapp a couple times now and have not found it to be a particularly friendly experience.
I got a free Google Voice number and might use that in the future, but I had to tie that to another US-based phone number. What will happen if someone else starts using that number, especially if they also connect a Google Voice account to it?
I don't know that I have a better design in mind, but using a phone number as an identity has some nasty edge cases.