Travel / Using iPhone in Poland, which carrier to buy a SIM for? And other questions... [17]

hi. I have another question. i leave in Poland for whole my life and i wolud like to buy iphone 3gs the new one. but i dont want to but here because it's so expensive. so i've already found i phone in USA in apple website. but i am not sure that if i buy it will be working in my country?? or i should to use first card from At&T and after from my country for example Play Fresh?? or i can buy in this website unlocked this mobile? i hope you understand my question and help me.... Best regarts Natiis