A prototype 64GB Apple iPhone 4 has reportedly been leaked from Foxconn factory in China, but don't expect to see it on retail shelves soon. It could just be a phone for test purposes and not for sale.
While Apple has yet to announce the new iPhone (which may be called iPhone 5), it seems that a prototype of a 64GB iPhone 4 has been spotted at a Foxconn manufacturing plant. According to a Hong Kong-based website, you would notice that the phone (above picture) has its storage capacity and model number marked with "X"s.
The prototype phone claims to be running iOS 4.1, and not the latest version 4.3. Regardless, it is unlikely that Apple will go mass market with a 64GB iPhone 4 as it is probably too expensive, and that the new iPhone 5 could be announced soon. The current Apple iPhone 4 comes in 16GB and 32GB configurations.
Source: Apple Insider