What does the iPhone 3G have that the iPhone doesn't?

Honestly, there aren't many as the iphone 4 has major improvements over the 3G. The Antenna issue is very small and only affects a few users in the United States due to AT&T's extremely bad reception. If you're planning to get an iphone 3G, get an iphone 4 instead, if you don't mind coughing up a little more money.