switching carriers ipad 3
OK I returned my Ipad3 WiFi to get another Ipad3 with cellular, I have read that the Ipad is not locked to one carrier and can be switched. What I need to know is this true? The two carriers in question are AT&T and Verzion, If I buy an Ipad3 with AT&T and dont like the coverage can I switch to Verzion or Verzion to AT&T?
I have searched the subject but dont have a clear answer. I have also read you cna go from Verzion to AT&T but not AT&T to Verzion.
Please set me straight