I currently have the Rezound and can only use FoxFi in bluetooth mode? If tethering is disabled like the Rezound, no expandable memory, removable battery, and possibly poor battery life, then I'm out.
Interestingly, I'm using Clockworkmod tether connecting to a linux machine and it works without any problem. Based on this, I'm would guess all USB tethering would be fine. I am waiting for a more reliable root method before trying the wifi tethering options.
