iPad Air Verizon vs AT&T vs T-Mobile vs Sprint can I use SIMM from any on another?

Everyone is feverishly asking if it's possible to use AT&T iPad Air with a Verizon SIMM or vice versa, a Verizon iPad Air with an AT&T SIMM?  How about a T-Mobile on a Verizon iPad and vice versa?

First lets clarify some confusion with 3rd generation and 4th generation iPad.  While it is true you can purchase an Verizon iPad and use an AT&T ximm card in it, you will only achieve the 3G or 4G speeds available on AT&T -- not AT&T's LTE speeds.

With iPad Air (5th generation), are iPads all the same model hardware and they are only differentiated by having the corresponding telco's simm card in the device for your convenience.  To confirm, this statement here is screen shot of Apple's web site on their LTE coverage vs. iPad model.  Notice how only one hardware model of iPad Air exists for all LTE telco's on the right.

When you compare this to iPad 4th generation, there were two hardware models as shown.

So in summary, no matter which iPad Air you purchased you do not need to swap the hardware to be compatible with another carrier's LTE network in the US.  Simply get the correct sim card and activate it.