Are there 2 different iPhones

No. There are millions of different iphones. Just kidding. There are currently 2 iphone models that were released in the US - a 4 GB model and an 8 GB model. The 4 GB model was the original release, and has since been replaced with the 8 GB model as the sole iphone being sold by the manufacturer in the US.

Don't forget about the NEW iphone 3G..... that came out 7-11-08

Well, now there is also another type. The iphone 3GS. But that was only recently released.