Yes, it is a knock off. I am 100% sure. Do not buy from them. Only 2 providers have contracts for iphones, verizon, and at&t. If you want an iphone, buy it from one of their stores. As an at&t customer I personally recommend verizon.
There are no slots in the iPhone. I wouldn't trust any online site besides eBay and amazon and even with those I read descriptions very well and look at pictures. If the price is too low to be reasonable then most likely it's either a scam or a knock off.
I bought mine for $199 at Verizon when I updated my contract. You maybe be able to get it cheaper there, I don't know. Which even that is a great price. It's like a mini computer in my pocket at all times. I have unlimited data and it's just a great phone. I have the iPhone 4. The 4s is out and it's an upgrade. I don't know if Verizon has the 4s though. But the iPhone 5 is coming out after Christmas.