I currently have ATT (5S) for my main phone service. I have a iPad mini and an iPad Air both which are cellular. The mini is from Sprint at the Air is from ATT. The sprint iPad has a 6GB plan currently active and the ATT one has nothing. What I want to do is take the Sprint SIM and use it in the ATT iPad but that doesnt work. I was under the impression they were all unlocked. My iPhone 5S ATT SIM works fine in both tablets. Is there any thing I can do to get the Sprint SIM working with the ATT iPad Air? Thanks.