As reported by MacRumors, the unlocked, carrier-switchable SIM cards built into the newest iPads aren't necessarily so -- at least if you buy them from an AT&T store. Though the card comes from Apple with the ability to support (and be switched among with software, if a change is necessary) all major carriers, "AT&T is not supporting this interchangeability and is locking the SIM included with cellular models of the iPad Air 2 and Retina iPad mini 3 after it is used with an AT&T plan. ... AT&T appears to be the only participating carrier that is locking the Apple SIM to its network. T-Mobile's John Legere has indicated that T-Mobile's process does not lock a customer in to T-Mobile, which appears to be confirmed by Apple's support document, and Sprint's process also seems to leave the Apple SIM unlocked and able to be used with other carrier plans. Verizon, the fourth major carrier in the United States, did not opt to allow the Apple SIM to work with its network." The iPad itself can still be activated and used on other networks, but only after the installation of a new SIM.