So, I was planning on getting an AT&T iPhone off eBay. I wanted to use Straight Talk on it, so I could save money in the long run, rather than get a contract. Now, I'm unsure which model of it I should get. I'd like to be able to use iOS 6, so an iPhone 3GS/4/4S would be my options. I'm willing to spend around $400 on the phone. What would be the best option for my price range? I was going to probably use it for 2 or 3 years then I'd upgrade to a new phone. Thanks everyone.