The rational design of the iPhone 3G. The iPhone 3G and the iPhone 2G are similar in appearance, but they are different in internal parts layout. The iPhone 2G had main parts mounted on both sides of a frame in the center of the chassis, while the iPhone 3G has the parts piled on the back cover of the chassis. In addition, the back cover of the iPhone 3G chassis is made of resin, allowing a more flexible layout of the antennas and making it possible to include a main antenna for W-CDMA and GSM and a sub-antenna for wireless LAN, Bluetooth and GPS at different locations. In the iPhone 2G, which had a metallic back cover, antennas were concentrated on the bottom of the chassis. In respect to the Li-polymer secondary batteries, both of the models are equipped with battery cells simply wrapped in a laminated film. Though there was no description about the battery capacities, but the volumes of the two batteries are almost the same.