Please note that if you purchase an iphone in a different country, you 'may' have issues with the warranty. The guide line is that the warranty is valid in the original country of purchase. So if you have to make a warranty claim the phone would need to be sent to someone you know in the US for them to take to Apple and then they will need to send it back to you. This will be at your expense.
Good luck.
I'm absolutely aware of this 'warranty issue', but the fact is, it is still worth for me to buy unlocked iPhone in US, and then cover the potential cost of repair, than to buy unlocked iPhone in my country. 16GB iPhone 4 is like $1100. That's crazy.