I read on one of the updates for Foxfi that it will no longer work on phones running the latest versions of Android. I want to say it was anything past 4.1.1???? I know I can't use it now on my Galaxy S4, running 4.2.2......:-(
Foxfi was working on my Razr with 4.1.2 (I think, it took a swim, so I can't check, but it was fully up to date with OTAs), though it was doing something through a VPN setting.
Just a note: if you want wifi tether on the Ultra/Maxx, there is a simple root process, followed by fairly simple instructions where you change a single setting to allow the stock tethering to work. You can then un-root if you want. I then downloaded a tether widget, so a single click on the widget and my tethering is active. Brilliant!
Foxfi was updated today, it now works on the Ultra. There is one additional step when you activate it but it's straight forward and works like a charm now
Edit: I have unlimited on Verizon in case you're wondering