Since this post was already necro’d 
My experience from UE3, is that it’s really quite simple, as far as the Unreal networking goes. Simply open a server on one device, and connect to it in the usual way on the others, and it just works. Now, as points out, you may have fairly significant issues with actual networking layers, in discovery and actually making the connections through firewalls and such. Gamespy supplied functional discovery services along with NAT traversal, if I remember correctly, that allowed for that stuff to work well. While we don’t, as far as I’m aware, have any particularly good matchmaking/master server type services that provide cross platform support, for the basic usage of it, if you’re using a server that is out in the world, it should be really easy.