@trwnh the "trick" with webfinger is that it's a way to go from a "name" to an authoritative context (the authority for "x@y.xyz"' is "y.xyz" and the authority for "blah.com" is "blah.com"; the challenge with phone numbers is that it's impossible to infer the authority for +1-416-867-5309 / telcos don't provide a lookup system). That's really it; the rest is a cultural thing.
@blaine there might not be an authority for a phone number but i think it can be handled more like a combo of "local dns resolver" + "registry of phone number". sure in many cases with identifiers that have an authority component you can just use their webfinger if they have one, but i think it would also be cool to be able to use your own webfinger and "proxy out" as needed, in the same way that dns does it