I'm with Verizon two of my phones uses sims and two doesn't, so the sim can go either way with Verizon, if it takes a sim just pop yours in and your good to go, if it doesn't then you have to program it or take into store or call if you don't know the program process.
the verzion one don't take sim it's cdma but the at&t's are gsm they take sim card they can work with anything with sim card i been learning about them on youtube.
Can you please tell me what is a wall wart, you said it in your description and in update? All so iphone 4's do take a sim card but maybe because you bought this phone through Verizon they don't use sim cards. I have a iphone 4 through AT&T and wasn't purchased thru them but it stll takes a sim card. On yours if you check either side there might be a silver looking line if you grab ahold on it the tray will come out if your indeed does have a sim card holder. Great auction though hope you get alot of bids! ;)