The latest update to the iPhone firmware hints at a new model in the works. Within the code Apple has always used different numbers to represent the iPhone models. For example, "iPhone 1,1" is the original iPhone while the 3G iPhone is labeled "iPhone 1,2". The new label is now "iPhone 2,1", and confirms a change is coming soon. If Apple is using the same schedule it has used for the past couple of iPhone releases, then we could count on a June or July release.
Mac Rumors also notes that:
"Meanwhile, at least one developer has noticed actual "iPhone2,1" models in use based on PinchMedia ad serving reports. (Other numbers blurred out)."