I bought an Iphone from someone and when i press the circular button at the bottom, even when i have my simcard in, it asks me to connect my iphone to iTunes. I dont have internet on my phone plan and i want to keep my phone plan the same price. How can i unlock the Iphone without activating it or connecting it to iTunes?

I want to get an iPhone this month but my contract won’t be up until December.. How do I get an iPhone without having to pay a lot extra because my contract isn’t up?