I've been trying to set up personal hotspot (tethering) from an iPhone to a MacBook Pro. It works OK using WiFi, but I want to use USB to lower the power requirements, let the phone charge, and make it easier for the user, so it's just a matter of plugging in the USB cable to make it all go.

The problem I'm having is the iPhone doesn't show up as a network interface in the Network System Prefs pane.

-Tried an iPhone 4 and a 4s - both running iOS 6.0.1
-MBP is running OS X 10.6.8 (Snow Leopard), all system updates up to date.
-iTunes 11.0.1, which installs AppleUSBEthernetHost.kext 2.3.6 (which comes up several time on the web as a possible problem, but doesn't seem to have fixed it in my case).
-Tried PRAM Zap, Permissions repair, fsck
-Both phones are on Vodafone, one post pay, one pre pay.

I'm out of ideas. Has anyone done this successfully? Have I missed something really obvious?