You cannot use a CDMA Verizon phone on straight talk. I know this because I have an iPhone on straight talk. It has to be a gsm phone because you have to order a micro sim from straight talk. Unless you buy the phone retail from straight talk which they do sell now. But a iPhone coming from another carrier has to be GSM. I think however that 4s is a world phone and has a SIM card to so as long as the iPhone has a gsm antenna your good. Otherwise no