On the picture below you can see the first iPhone and the new 3G iPhone side by side. To be more precise it's a model of the 3G phone. According to the original press release, the new handset is a bit thicker, which is in fact true, but only in the center of the phone. When going to the two sides the 3G model gets slimmer, it looks smaller in volume than its predecessor. Thanks to the convex back, the new phone provides a better grip.
Translated by Szaszati