There are a couple of awesomely useful things you can do with the recent calls list on your iPhone.
What? They're my recent calls, guys. I know, I know, the blurring's taking up most of the shot, but whaddya expect?
Anyhow, if you touch on the blue arrow (indicated in my screenshot above) next to a phone number or the name of a person who called you, you get some pretty handy information. Of course, you can create a new contact from the number or add it to an existing one, and you can share the number through email or a message right from that screen, too. I find that especially useful if I need to pass along a number but don't necessarily want that person in my contacts list. (Apologies go out to the guy I was thinking of when I typed that.)
There are a couple of options that I think people don't pay attention to, though. One is obvious but often ignored, and the other is more hidden. The obvious one is that your iPhone tracks your call time.
If you're the kind of businessperson who needs to keep tabs on who's calling, how often, and for how long, this is just peachy.
The second, less obvious thing you can do here is touch and hold briefly on the number at the top, which'll bring up a Copy option.
Why would you need this, you ask? I use it when a number I don't recognize has called me but hasn't left a message, especially if it's toll-free or from outside of my state. That way, I can do a Web search for the number and see if anyone's made telemarketing complaints about it. I can also see if the number appears on someone's site so I know who called—I'm sneaky like that.
In any case, it's great not to have to remember the number between the phone interface and Safari, especially for poor forgetful souls like me.