did you do a PRL and profile update?
if you did not,, go to settings and "system updates" and do a PRL and profile.
also, have you called sprint? its possible your account is not set up.
if all of that has been done,
give them your zip code and see if there is an outage in your area. could be LTE upgrading going on and mobile service could be TEMPORARILY interrupted.
this is an easy fix so no worries....