I have a question about Multiplayer Tutorial in Unity3d web site.
Multiplayer Sample (StarTrooper) can be a Network connect in the same Wifi.
But it is impossible to network connect in other Wifi( or multiple network).
It is impossible to network connect in between Wifi-3G.
Why not?
In the same wifi : your network is only local. It is possible to have a network working in Unity outside your local network. For example, you can set up a server with your own computer (same way as for a local network, but you have to open the ports you use on your firewall) that can be connected from outside using your external ip.
Examples of ip :
127.0.0.1 = home = network on the same computer (useful for testing purposes)
192.168.0.1 = local network adress of several computer using the same internet connexion
56.47.120.85 (it can be anything 
) = external ip people use to connect to your computer
To know your ip adresses, go to command console in Windows (research cmd) then type ipconfig/all inside this console
Hope it helps 