Activate sprint iphone 4s at verizon?

My friend gave me his old iphone 4s but he has sprint and I have verizon. If I take it to verizon will they activate it and if not why? Also if they won't activate it is there anything I can do to change it to verizon?

The phone has to be unlocked first. The sim card has nothing to do with it. Unlocked means the phone was programmed to only use Sprint's network and no others. That's why it says Sprint in the corner on the screen. If it is unlocked it can be used at any carrier you choose. Yes, it will work on Big Red too. Both of those networks use CDMA signals so there's no problem. You can find unlock codes online from vendors. A lot are scams but you can find some that are legit but it will cost a few bucks. Best luck.