Iphone 4s switch from Verizon to straight talk?

I recently came into the possession of a Iphone 4s. I know the guy who owned it and he owed me some money, so blah. Anywho, I'd like to switch it from verizon to straight talk since I'm going out of state soon. I have never owned a smart phone before, so I don't know where to start. Any help?

Before you even start, make sure the phone is not blacklisted and your friend didn't just hand you off a dead paperweight that can't be reactivated. Verify that here:
http://myimeichecker.com/
If it's legit, check to see if the serial number will switch to them using their page here:
http://www.straighttalkbyop.com/
If you can't there, try here.
http://www.net10byop.com/
Between these two and a new sim card, you should be fine. Best luck.

Obviously call straight talk if they are the ones you want to sign up with.