If my memory serves me right, you can sync your iPhone to iTunes- putting music and apps and information on it. But only while it's plugged in and on Wi-Fi.
Well, if it has to be plugged in, and on Wi-Fi, common sense would tell you just to plug it into your computer and save battery life.
I'm here at the library, I want to add music to my iPhone, but I don't have my cord. Will I be able to add music to my iPhone from my laptop in the future? Is it just a matter of time?
You can do it right now, the iPhone does not need to be plugged into a/c power to wifi sync. It is just recommended especially if the battery is low. But this is not cloud syncing, this is local still. Cloud would be if your songs were all stored with Apple in iCloud and you could pull songs down from there over 3G even.