I am kind of amazed that that works. What's going on - does the baseband have its own IP stack, which it somehow shares to the computer, which then declares its own mini-lan and lets the iPhone on at a higher level such that iOS uses that preferentially?

That's bizarre; I'm tempted to try it out when I get back to a country in which I have mobile data.

"More happening in this iPhone, I feel, than has been revealed"