The oddest iPhone omission is cut, copy paste.
The omission I am most disgusted by is an API that would allow Google to sync the iPhone calendar to Google Calendar over the air.
The second oddest iPhone omission is that you can't lock the touch screen during a call. I frequently tap the wrong button. I'd like a way to set the screen to 'swipe mode' so it was safe from errant touches.
Update: I just tested with iPhone 2.2. If I click the 'off' button during a call, it locks the screen just the way I want. I'd tried this with 2.1; it seemed to work but it on one test it disconnected me. So I gave up on it.
On the other hand 2.2 also rebooted during a call when I wasn't touching that switch, so I'm not sure I'd recommend upgrading just yet.