Mac Rumor posted a story that new "iPhone 4S" part images from iPatchiPods suggest that the iPhone 4S will look much like the iPhone 4, but with some notable differences in the frame.
The mid-frame images above show that this so-called iPhone 4S will have two antenna breaks at the bottom of the casing. This differs from both the AT&T (GSM) iPhone 4 and Verizon (CDMA) iPhone 4. In AT&T's iPhone, the antenna breaks are in two spots, along the lower left side and top left sides. On the Verizon's model they are both at the top sides of the casing.'iPhone 4S' Casing Resembles iPhone 4 with Some Antenna Changes
The reason for the movement of the antenna breaks is to accommodate different frequencies of the different mobile technologies. This "iPhone 4S" appears to have a slot for a SIM card, suggesting that at a minimum it will support the GSM standard like the original AT&T iPhone 4. It is believed the iPhone 5 will support both GSM and CDMA, but we haven't heard anything definitive about the band support for this iPhone 4S.