a smaller sim would give the phone more space to more things in. also they could have used micro sims causethe iPad was never meant to be used as a phone, and the micro SIM could have been chosen to keep you from popping your iPhone or other smartphone SIM in it and avoid paying 2 data bills.
The regular sized SIM still makes sense in a phone because their customers would want to be able to use SIMs from old phones, or put their SIMs in another phone should the need arise. They won't want to take away that selling point (Apple may not care but ATT probably does)
The real red flag here comes from redundancy. If the back is truly removable, revealing the SIM tray, why is it also accessible from outside (and the side no less). Apple wouldn't go for that, especially since they'd have the opportunity to make the side all nice and smooth if the SIM could be accessed from within
A. apple likes to make new standards
B. space
c. unlocking. they just officially unlock it then put in a microsim to make it almost impossible to get another carriers sim in.
D. the iphone. make it so you cant put your iphone sim in.
they can give this phone microsim for A,B,and C
also some people say att wants all there new things to be microsim and what way better than to use the killer ipad,iphone to start the trend?