Tracking position in 3d on mobile similar to Project Tango's SDK

I'm looking to try to use full 3d positional tracking on iphone. Reading Google Tango's documentation, it appears that this is possible using both motion tracking + camera using a method called visual-inertial odometry.

"Tango implements Motion Tracking using visual-inertial odometry, or VIO, to estimate where a device is relative to where it started."
https://developers.google.com/tango/overview/motion-tracking

I would love to be able to implement this on both iphone and android using Unity if it's at all possible. It looks like there is a Tango Unity SDK but it may only support android devices.

https://developers.google.com/tango/apis/unity/

Anyone know of any way I could try to implement a method similar to the above that is capable of tracking mobile position in 3d? It doesn't have to be Vive level of precision but close enough would be great.

 

Looking into this a bit more, it appears that a Tango enabled device will require new depth sensing hardware so my guess is that this is not currently possible on any phone. Someday...