Well, I wouldn't call it a fake... it's just not an iPhone.
And they don't say it is. Actually, the explicitly say that it isn't.
Dual SIM? iPhone doesn't have that
Java? Not on an iPhone
Memory Card? The iPhone doesn't have that.
If you read the description, you'll find the following sentence: 'Note: This is not an Apple iPhone".
So, it's not a fake, but it's not the real thing either.
The design is very similar, so if you flash it around a bit, people might think it's an iPhone 4.
But as it runs under Java, you'll probably notice it to be very slow and unresponsive, the touchscreen will react badly, etc.
Also, these things tend to fall apart within weeks of buying.
Warranty? Forget it. The seller is in China.
That should answer it...