If you are looking at getting one of those, just watch that they:
A. Don't scam you. they could do this a number of different ways: Low quality crap, something that just doesn't work and they don't want to refund your money, or not shipping it at all and having no contact info. I bought a 8gb mp3 player for 20$ and it turned out to be crap, I formatted it to see how much memory it had and it wouldn't boot after formatting. Lucky it was 20$.
B. That it actually works on a carrier. My friend has a knockoff Iphone, it's on T-Mobile, so you have to look at that as well.
My opinion, don't get one of these when you could get the real thing and have no worry about quality or other weird mess.
Hope this helped and good luck