ZiPhone found references to a chip called the SGOLD3 in the latest iPhone SDK, leading many to believe that this represents a new 3G chipset for the upcoming 3G iPhone.
While it's not unheard of to see references to unreleased chipsets buried in Apple's software, it seems the interpretation may be a touch optimistic.
First, people have been quick to presume that the "SGOLD3" refers to the SGOLD3H (PDF) chipset, which is a HSDPA 3G chipset, but the actual SGOLD3 (PDF) chipset is not (although a UMTS coprocessor can be added to it).
Finally, there also appears to be a reference to SGOLD1 -- an older chipset that the iPhone presumably does not use. This could indicate that the code is simply generic placeholder code, rather than reflecting any specific plans.