What's the difference between the iphone and the "clone" phones?

I was shopping on ebay and they have a cell phone that looks like a iphone but isn't an iphone. It looks as though it does the same things and works the same. So is there any difference besides the name and price??? Has anyone owned one before or now???|||I know that there are a lot of iPhone-clone in China. The OS of most of knockoffs called MTK. Some are using Windows Mobile or Windows CE.