[Lizard]

Yes, curt.clifton and whpalmer4 are basically correct. The only detail I would add is that not only do the iPhone and Mac need to be "local" in a geographic sense, they need to be "local" in a networking sense. For most people, this means they need to be connected to the same WiFi base station, or you need to turn on Internet Sharing on your Mac and connect to it from your iPhone.

(There are some more complicated configurations that could work, but that's the sort of thing to ask a networking guru about, not Omni.)