I know I'm overlooking existing infrastructure and countries with fewer smartphones but we need to leave this behind at some point.
Without each side being unique, how would voice://John_Smith-00003475 be better than a phone number? We already have address abstraction in the form of contact avatars on our phones. Click John's face, then talk. And since this is done locally, I know that a wrong number is just my fault and easy to fix. Choose any reason why a central or even distributed resolution contains an error and suddenly you're back to keying phone numbers just to make a call while we wait for corrections to be issued by, whom, exactly? My parents don't even know the difference between a cellular connection and a WiFi connection on their phones, are they supposed to be responsible for their own online contact records too?