Because it is web based, it is global. The web is a country on its own. As long as you can come online is all that matters. The phone calls are free.
We would have to agree on industry standards so that numbers don't get duplicated anywhere. If we could do this, voice would overtake video as the fastest growing segment of internet traffic. People want to talk to each other. That would be a contribution to world peace. I thought it was Chatroulette, I was wrong. It's the smartphone, the kind that makes and receives free phone calls globally.
Voice is just data. There is no reason whatsoever why phone calls need to be any different from emails. You send and receive as many as you want. Email addresses don't have area codes, country codes, none of that nonsense.