BGR is reporting that Apple will introduce a totally redesigned iPhone 5 in the last quarter of 2012. The phone will feature an aluminium back with a plastic or rubber bezel surrounding the front edge of the phone similar to the 3GS. They state:

"....it will join the glass iPhone face with a new aluminum back plate. It will also cover a redesigned antenna system that surrounds the device, allowing Apple to build the rear case out of aluminum without having to use a large plastic insert above the antennas as the company does on its iPad 2 Wi-Fi + 3G."