I was looking at iPads for sale on EBay recently and several are described as 'unlocked '. I'm not sure what this means. Does it have to do with whether the machine was assigned to AT&T or Verizon from the factory, so that unlocked means it is unassigned? I know that when I have gone to buy cellular data plan time my iPad directs me to AT&T . But it also looks like I could deal with Verizon or another carrier if I wished.