Can my sim card from samsung work in an iphone?

I have a samsug galaxy s2 from straight talk. It uses at&t towers. So my friend is gonna give me his old iphone 4s. Can i just switch the sim cards will it work? I also pay for data and stuff.

If your friend's iphone 4S is network unlocked or on the same carrier as your sgs2, it will work. Also, be sure to get him to turn off Find My iPhone before giving it to you. If not you won't be able to restore the phone.

No your galaxy s2 uses a regular sim card and an iPhone 4s uses a micro sim card but if you take it to an at&t store they can switch it over for you free of charge and transfer your contacts and everything fast and easy