The iPhone 3G's back features a redesigned plastic polycarbonate housing, replacing the aluminum back from the first generation. The buttons were also made from plastic to metal, and the edges of the phone were also tapered, providing a better grip of the phone. The iPhone 3G also introduced colors to the iPhone bringing black and white backs to the device. However only the 16GB version was available in both colors. The dimensions of the iPhone 3G were slightly larger than those of the original iPhone. It was 4.55 inches (116 mm) high, 2.44 inches (62 mm) wide, and 0.48 inches (12 mm) deep, compared to its predecessor, which was 4.5 inches (110 mm) high, 2.4 inches (61 mm) wide, and 0.46 inches (12 mm) deep.

A rear view of the original iPhone (left) made of aluminum and plastic, and the iPhone 3G, made entirely from a hard plastic material.[16]