Yeah, iPhone will most likely get an update to the iPhone 4 this year, but I really doubt it'll be a new generation, like iPhone 5. It has to be a minor upgrade to the iPhone 4, improved camera, faster speeds, etc. Or perhaps additionally that "nano" iPhone.
With something like the iPhone 5, I'd expect substantial OS changes, something that would warrant an entirely OS version as well, like iOS 5. However, I've not heard of any developer betas for iOS 5, at least publicly released-betas, as of yet.
Back when iPhone 4 was due to launch in summer of 2010, developers got access to the iOS4 beta many months in advance. I remember by Feb. of 2010, Apple has already seeded the 3rd version of the iOS 4 beta out to developers. As of right now, all we have so far, is 4.3 SDK beta as the latest beta SDK.
This could change if iOS 5 was planned to be release at the end of the year, we'd receive beta kits in the summer, but I doubt any iOS5/iPhone 5 by summer release will happen. It has to be an incremental upgrade and/or another model-based on iOS 4.