the latest airvana has VoIP built in. Sprint does not currently offer VoIP.
IF you put the Airvana IN FRONT of the router, the Airvana has the potential to hog up a lot of bandwidth for nothing. this bandwidth is not used for mobile phone calls!
this is the reason why the airvana is put BEHIND the router.
the QoS (prioritizing) feature is ONLY for VoIP and NOT mobile phone use.
the restriction feature on spritns site is not working. do not even waste your time with it.