Is it possible to buy an iPhone in the us with a SIM card?

I live in Europe and I need a phone with a SIM card, but I want to buy an iPhone in the USA, where it is cheaper. I need to know if I buy will I be able to use it in Poland?

Iphone uses nano sim. You are right its probably cheaper because the dollar trades lower then the Euro, but don't assume the cheap price you see with a contract is your price, thats with a contract only.