My understanding is that Apple will be selling the LTE iPad Air (and presumably the LTE Retina Mini) preloaded with a particular carrier's SIM. Further, from what I can tell, the LTE iPad Air only has a single hardware model (A1475), with the only hardware difference between a T-Mobile iPad Air and a Verizon iPad Air being the preloaded SIM card. This leaves a few outstanding questions. 1) iPads are sold unlocked. Will you be able to insert a SIM from a different carrier and use it seamlessly with the device? In other words, will carriers support iPads originally sold for other carriers? E.g., can one buy a T-Mobile iPad and then insert an AT&T SIM and use it with AT&T? 2) If you *can* use an LTE iPad with another carrier's SIM, will the iPad's Settings-Cellular Data screen automatically display the correct carrier's plan options, based on the currently-loaded SIM? Or will you be forced to activate it through the new carrier's website (potentially with activation fees and the like)? 3) Will Verizon's 3G CDMA network work on another carrier's iPad? For instance, could I purchase a T-Mobile LTE iPad, decide to insert a Verizon SIM card, and then have the device fall back to Verizon's 3G Network? Note that AT&T and Verizon both use iPhone 5s Model A1533, but only the "A1533 CDMA" supports Verizon's 3G network. 4) Does the T-Mobile iPad support T-Mobile's HSPA network on 1700mhz? T-Mobile says it does on Twitter, but Apple's website does not include 1700Mhz for HSPA. If anyone knows the answers to these questions---and has the sources to back it up---please post. It would help those of us deciding which model to purchase. For instance, T-Mobile seems to have a very liberal policy on accepting customer-provided hardware, and will even provide the free 200MB of data to those users. If only the Verizon model supports Verizon's 3G network, I'd probably buy the Verizon model and immediately insert a T-Mobile SIM card. OF course, if only the T-Mobile supports 1700Mhz HSPA, then the T-Mobile model becomes more attractive. Further, if I'm unable to use the iPad's built-in cellular data plan tools with any other carrier than the original one, that would push me toward the T-Mobile model. Thanks for any help.