A good idea, but won't work in reality. 1) You'd need a directory of such numbers from every country. 2) For those where you have the number, IP-based country location does not work, so some people would get a wrong number.
I don't think needing a directory of numbers from each country is an insurmountable task for a company with the mission of organizing the world's information!
Actually writing a network spider and page ranking mechanism and chasing after an organisation in real life to keep contact details up to date don't have that much in common... It would work the same as in any other company - i.e. would require time and money.