Samsung has been putting a different letter at the end of each model number for different Galaxy Note 4 devices (it has been doing something similar with the Galaxy S5) so while someone might have the SM-N910T Galaxy Note 4 and you the SM-N910A, what is the difference? They both look the same, right? Well, it is a little more complicated then that. Lets take a look at the difference between the Galaxy Note 4 model numbers:
You can learn more about the difference between CDMA and GSM here.