Are there any VR headsets for iPhone that feature positional tracking?
So far the only VR headset I've found for the iPhone that does positional tracking is the Occipital Bridge.  It's $399 and it features inside-out positional tracking that doesn't require w computer.  It requires iPhone 6 or later running iOS 9 or later.  It ships in March but it's available for pre-order now.  I wasn't able to find any information on when exactly in Marxh it's shipping.

Other answers are welcome.