A code in iOS 4 reveals that the new iPhone and iPad models may be all set to begin field testing. The relevant code allows iDevices carrying the designations of iPhone3,2, iPhone3,3, and iPod2,1 to “auto-activate”, a process which allows carriers to test the devices without requiring manual activation through iTunes.

Similarly, the evidence that field testing of the iPhone 4 began in late November 2009, more than six months before its launch. New iPhone models carry the code iPhone3,2 and iPhone3,3 rather than “iPhone4,1″ which probably forces us to believe that the hardware is  nothing but minor revisions being carried out to the iPhone 4.

But still we can't make out "Why there are two new iPhone models in field testing" ?