I bought an iPhone and upgraded to a plan for iPhones 40 days ago.
My previous phone was a 3410 from Nokia with a GSM only plan (not even SMS!) so the upgrade was quite huge ;)
Everything's been told about an iPhone but I will tell you how I feel with it.

I) The present

1) It's so beautiful.
I am keen on gadgets mixing usability and art and I must say my iPhone is really the most beautiful I've ever had.
In the first few days, I was keeping on just looking at it and felt pleased.
The lines are so perfect, stripped down, "pure" that I don't know how one can be more beautiful.

2) being pervasive and unlimited mitigates how slow EDGE is.
Yes, EDGE is not the fastest and having Wifi on my iPhone is reinforcing this fact.
But coupling how pervasive it is and that it's unmetered makes me feel the biggest value similar to the transition from dial up to DSL : you don't even think about connectivity, you don't hesitate to grab some news or a map when you want it, it's just there.

3) music and videos is great.

4) the internet eventually.
Since 2000, carriers has been stuck into the idea that you should need a language (WML) and a protocol (WMP) for what's via the Web on your mobile.
Surfing the Internet on my iPhone definitely trumps this idea off !
The navigation is really simple, double tapping is smooth.

II) The future

When you're working in this industry and once you tasted an iPhone, the tough question came around : how to make this better ?

1) Short term.
At least 4 better are obvious and easier predict.
i) Faster cellular : HSPA then LTE...
ii) Better camera : 3 then 5 then 8...
iii) More memory : 16GB then 32GB the...
iv) More precise location : cell triangulation then GPS then...

2) Mid term
It became there harder to say.
v) NFC : to pay or pass gates with your iPhone.
vi) Automatic wireless connection to a bigger screen or keyboard : this will come but may be dangerous for Apple because it will put an iPhone in a competition with laptops and desktops for persons in the mainstream.
vii) Automatic wireless backup to a bigger and safer memory : would it be at home or at Apple's ?

3) Long term.
Somewhere in 2009-2010, an iPhone with the previous will come out ; it will be engined by a chipset as Moorestown from Intel, fast enough to do most of what the mainstream want.
It will be the ultimate monolythic-and-carried-in-a-pocket computer, to get only smally better.
Here will come the need for a new era, more than personal, not monolythic, not carried in a pocket, the first symbiotic computer.