I only bought my 3G last November, so it will still be over a year before I'm eligible for a subsidized upgrade. Near the timeframe of a June 2010 iPhone refresh if Apple continues releasing an upgrade in June of the year 🙂
I just hope that Apple continues to at least make the previous generation relevant with a software refresh. At some point, you have to figure the 1st generation will not be able to keep up (MMS? Though that is probably not a hardware limitation). Next generation, more RAM? Hopefully apps won't require it until at least 2010. Video? I occasionally used it on my previous phone, and wouldn't mind it, but I can live without it.