The phone number is a backwards compatibility feature. We have modern ways of locating a user (see SIP, Email), but those won't be compatible with POTS.
The use case here, Apple's iMessage, in fact allows users to use alternate methods of user lookup, including multiple email addresses.
If you don't find it acceptable, what do you propose as an alternative?
> If you don't find it acceptable, what do you propose as an alternative?
So far, the best alternative for id that I've found is...
Email address.
It's highly available, free to create, and you can pick your own letters/numbers that are meaningful. It can even be your name. Definitely better than phone number digits at being an id that I can share with my friends or those who I want to be able to contact me.
(For voice calls, I primarily use FaceTime Audio because they support email as id. But I also have skype, voip number for backwards compatibility, etc.)
Phone numbers are portable between providers, email addresses are not. So email addresses make worse identifiers (where consistency rather than encoded meaning is the important thing) than phone numbers.
(Also, the "pay to get a randomly assigned number" isn't always true: my Google Voice number was free, and I got to ask for particular digits string to be included and got to choose from a list of numbers that met that requirement.)
The use case here, Apple's iMessage, in fact allows users to use alternate methods of user lookup, including multiple email addresses.
If you don't find it acceptable, what do you propose as an alternative?