I have the second generation iPhone with no plans to change at the moment.
My son gave up on his iPhone and bought an Evo 4G after getting too frustrated with AT&T's dropped calls. Service in this area isn't bad, but if the iPhone ever supports Verizon, that may be motivation, along with all the newest features, to buy a new one at that time.
No plans to buy an iPad, either. It seems too redundant to the iPhone for my needs.