@evan I can talk to anyone in the world with it, if I'm willing to deal with longer names. That's the only argument about phone numbers that matters, and it applies to IRC, doesn't it?

People care about features and POTS doesn't have good features. I'm not sure what you're angling for with this line of questioning, but to me the conclusion to be drawn is “federation on its own is not a selling point if the system is lacking the features people care about”.