> I don't agree that phone numbers are good for onboarding: sending the first message to somebody on whatsapp requires asking for the phone number. Sending the first email requires asking for the email. Sending the first Skype message requires asking for the username. Not much different.
The argument for phone numbers is that you probably already have the phone numbers for your contacts, and not their Skype username if you've never contacted them on Skype before. It allows easy transition of contacts from the unencrypted phone network to encrypted messaging.
But it's still not clear what the issue is with at least having the option to use an email address instead of a phone number, which you also might already have in your contacts before the first time you communicate with them using a new messaging app.
The argument for phone numbers is that you probably already have the phone numbers for your contacts, and not their Skype username if you've never contacted them on Skype before. It allows easy transition of contacts from the unencrypted phone network to encrypted messaging.
But it's still not clear what the issue is with at least having the option to use an email address instead of a phone number, which you also might already have in your contacts before the first time you communicate with them using a new messaging app.