Apple knows by now developers love nothing more than to deep dive things like the just released iOS 4.3 beta looking for hints of next-generation iPhone 5 and iPad 2 models -- and guess what? Found them!
GSM iPhone 4 is iPhone 3,1 and Verizon iPhone 4 is iPhone 3,2 -- so what then is iPhone 3,3? (Let the T-Mobile or Sprint rumors start!). There's also iPhone 4,1 and 4,2 which should be the iPhone 5 in GSM and Verizon flavors, and the jump in model numbers indicates there'll be some improvements to the chipsets at the very least (iPhone 2G to iPhone 3G wasn't considered a full version jump by Apple, but iPhone 3GS was).
There's also iPad 2,1, 2,2, and 2,3 which should include Wi-Fi, GSM, and Verizon models as well.