Because the Verizon LTE iPad is a world-capable device, it has support for GSM bands as well as CDMA for the 3G fallback when no Verizon LTE is available. That means that you can use an AT&T microSIM in the Verizon iPad and get 3G HSPA+ data speeds through AT&T. This is a terrific option for those that have an unlimited data plan with AT&T: you can still use and pay for Verizon LTE when you’re in an area that has it (it’s very easy to toggle the data on and off in the settings), but you can also take advantage of your AT&T data plan (especially if it’s unlimited) by popping in a microSIM. If you don’t have a microSIM, you can cut your regular SIM to the right size, then buy a cheap microSIM adapter for when you want to put the SIM back into your phone. That’s great flexibility.
We should note that because AT&T LTE requires both the 700 and 2100MHz bands (the Verizon iPad has just 700MHz) you won’t get AT&T LTE on the Verizon iPad using an AT&T microSIM. Also, on the reverse end, don’t expect to get Verizon 3G or 4G on the AT&T new iPad because that model is lacking CDMA, plus a Verizon microSIM won’t authentic properly to get access to the LTE network. Confused? Just go with the Verizon iPad, unless you have AT&T LTE in your area.