For quite some time now it has been my plan to replace my three year old original iPhone model when this year's model comes out. For the past few months Chris and I have been in an ongoing debate, as he has somehow convinced himself that Apple is not releasing a new model this year. I'm not saying I know for a fact that they are, just that there's no way he can know for sure that they're not - especially since it has been their consistent pattern for the past three years to introduce an updated iPhone model every June. It's only April, and Apple has given no indication that they plan to break that pattern this year.
But there's another reason why I think he's wrong. As shown by their continued advertising efforts, Apple would still like to convert more consumers into iPhone users. But someone who is looking to purchase a new phone this year is not going to buy an iPhone 3GS that is already a year old, when there are other newer smartphones out there... like the Motorola Droid and the HTC Hero. Apple would be stupid not to entice those people with a brand new model of iPhone that surpasses these phones in performance.
Either way, once we know for sure one way or the other, I intend to upgrade my phone to the newest iPhone model available, whether it's the 3GS or a brand new 2010 model.