It's said to be the next iPhone - presumably the iPhone 5. Look for a slimmer profile and larger screen size, says analyst Ashok Kumar in a research note (via CNET). Also, the upcoming version, expected to come out next summer, is likely to have 4G capability. From CNET:
Another source, who I spoke with this week and who claims to have knowledge of the redesign, said the iPhone 5 is a "complete redesign. This is a very large project that Steve dedicated all of his time to. He was not that involved in the 4S because his time was limited." That makes sense to me. Cosmetically, the iPhone 4S is identical to the iPhone 4. So no big change here. And though the 4S has been revamped on the inside, in some respects, it carries over technology already in the iPad 2: the same dual-core processor, same memory capacity, same accelerometer, same gyroscope, among other similarities.