i'm planning to get a cellular iPad Air soon. is the Tmobile 200mb/month free legit? or is it a scam? seen stories about $10 charges, etc. if I get a Tmobile one from the Apple store, can I switch to ATT just by going in to the ATT store and getting a SIM from them? one of the "geniuses" at Apple told me no, but I suspect he was lying as per company policy.