So the one mild criticism I have about the iPhone thus far is that the phone functionality isn't quite as front-and-center as you'd like it to be. Remember Jobs' line about "calling someone is the killer app"? Well, I'm not quite sure they've got it exactly right yet. But I have an idea for an easy improvement that would really make a difference.
Here's the problem. If I was last using a non-Phone application, these are the taps it takes it takes me to call my wife:
1. push the home button to wake the iPhone up
2. "slide to unlock" on the screen
3. push the home button again to get back to the main application screen
4. tap the phone icon
5. tap "favorites"
6. tap my wife's name
On my old Nokia, I could generally get to my wife's number (assuming it was recently dialed) in 3-4 steps, even if I'd left the phone running the Gmail app. My gut is that 6 steps is asking a bit too much for calls you make ten or twenty times a day to your core group.
So here's my solution: double clicking the home button automatically takes you to the phone favorites screen.
If the phone is off, you'll still have to do the "slide to unlock" move, but even then you'll be always be three taps away from your top ten favorites. And if you're working in another application, two taps will do it (counting the double-click as one gesture.)
I'm wondering if there's a reason Apple didn't allow double-clicking of the home button -- the double tap is a pretty key element of the multitouch UI.