Apple is generally pretty reliable in their update schedules, but the iPhone is selling rather well right now, so I doubt they have any significant plans to update it any time soon.
Also, most of the major updates take place around major events for Apple. So like the Mac World conference or something similar is when MOST announcements of new products or significant hardware refreshes take place.
About the only possible thing I could see being added, is some form of 3G support. Which might be useful if you really like to use all the multi-media functions of the phone to stream music and videos, etc, but is otherwise really not all that useful.
You might also want to think long and hard about having an all touch screen interface. If you have large and/or long fingers, and lack a surgeon's dexterity, you're likely going to end up pressing the wrong key more than once. It also takes power to run the sensors that make the touch screen work, so there goes some of the battery life... Same with all the other things that make the iPhone so neat and shiny. They will suck your battery dry in no time.
So, just be sure to give it a good long and hard think about whether or not the iPhone really offers you something significant enough over your current phone to be worth both the price, the service lock-in with AT&T, and all the other potential drawbacks like probably having to replace your battery every 6 months to a year due to the frequent need for charging. Don't get it just because it's shiny, new, and one of the latest status symbols for conspicuous consumers.
I'm not an early adopter. I?m considering purchasing the iPhone, but with my luck they?d come out with a next generation model the month after I buy it. Does anyone know if there is a new generation in the works or due to come out?