Answers: The truth is, the iPhone doesn't own 3G because AT&T's 3G network is a practical joke. This is why Apple initially tried to get Verizon to agree to transport the iPhone (it refused for a multitude of reasons). AT&T's coverage is amazingly slim. Beyond that, 3G drains your battery much quicker. The subsequent iPhone will have 3G.Because Apple didn't want it to dance 3G yet...
From what I hear Steve Jobs stated that he didn't believe the chips were "mature" ample for use, and it does affect battery duration more when you have 3G. That is why they put WiFi ini it, though, so at lowest you could have glorious speeds by that type of connection.
I would deduce that the next iteration of the iPhone will be 3G competent.