What is claimed to be a frame for the iPhone 4S has been discovered, showing a different antenna to the iPhone 4.
There are two breaks at the bottom of the casing, different from both the original iPhone 4 and the Verizon iPhone 4, which uses CDMA rather than GSM technology.
This suggests that the antenna in the iPhone 4S is different, possibly to circumvent the 'death grip' issues suffered by the original iPhone 4.
The real question is, though, are these cases for a new, low-cost version of the iPhone 4 that will sit alongside the next-generation iPhone, or whether they are in fact cases for the next-generation iPhone. According to the report, iPatch is convinced they're for a lower cost iPhone 4S, but we'll not know for sure for a while yet.