It might be a 3G verizon version. They don't have sim slots. Your box should say "3G Verizon" if it is that version. AT&T 3Gs have sim slots but the box doesn't say AT&T like the Verizon ones do.
And your pad would have the black insert on the top of the back if it's a 3G. Wifi only is all aluminum from top to bottom except for a center black apple logo.