It may not be as sure as we want it to be, but its most probable that the iPhone 5 will be presente don June 6th. Apple just sent an invitation for the WWDC, the conference where new iPhones were presented in the past.
It means that the new iPhone comes a year after the announcement of the iPhone 4, alltough there is not a word about a new iPhone. The WWDC is a conference for developers which work with iOS and Mac OS. Due to the recurring presentation of new iPhones, it is most known for new smartphones.
The iPhone 5 most probably has a processor with multiple cores, just like the iPad 2 an Apple A 5. Possibly, the phone has a larger screen that is predecessor. Rumors are that the handset has the same size, while the screen grows towards the edges. There are rumors that the phone has a NFC chip. We'll have to wait a few months until we know more.
Source: Intomobile.com