iPhone 4 help

I bought an iPhone from my friend, it was 50$ so it was a steal. I made a deal with her parents to buy the iphone. The iPhone is not blacklisted or anything and it is off contract since they switched to Verizon, the service bars on the top say "No Service" and the phone is not activated. I'm switching to straight talk and my phone met all the requirements and I wonder if I can activate it since I bought it off a friend.
btw straight talk has AT&T compatible sim cards and ulimited everything for a month I just need to activated it, and btw I'm 15. Lol
Thanks for the help!