iPhone 4S CMDA and GSM questions

[Almond Joy]

I just recently bought a iPhone 4S which has a sim card slot. When I checked the far top left corner where it has the bars , it says SPRINT. Its weird sprint is CMDA and doesn't use a SIM card. Why does this iPhone 4S have a micro sim card slot??

 

[fredecus]

I am pretty sure all 4s phones are made that way so that there is only need for 1 type of phone for all networks. For example the iphone 4 had 2 versions 1 with a sim slot and 1 without.