1. What is the cheapest and simplest plan for the iPhone?
2.Is there a place you can buy used iPhones?
3.Have you ever bought the iPhone? If so, what do you think of it?

Any additional answer will be great.
Thanks in advance.
I have a contract with my brother, me and my mom.

I already have a phone from at&t, so if I buy the iPhone will I be able to replace the phone I already have and keep it in the plan I have?

Also, how much do extra features like internet and the music on it cost?