I find phone numbers awesome because you actually "own" them to some degree. (i.e. you can take your number to a new provider). Moving to a different messenger app with the same phone number means I can at least still find some of my network there. Only email on your own domain would have that feature.
I don't really care if they sell my phone number, it's already out there, I don't consider it private data anymore.
Quite true. It would be better, though, to be able to use an instant messaging system using a simple identifier lie an e-mail address, as an alternative to a phone number. Simply because there are quite some people out there who mainly want to message on a computer, and want to keep only some kind of messages on their phones.
I don't really care if they sell my phone number, it's already out there, I don't consider it private data anymore.