iPhone OS 3.0: Spotlight search [screenshots]

Spotlight search is accessible by flicking the iPhone's home screen to the right (as if there was a home screen to the left). In addition to serving as a global search app, it can also act as a quick application launcher.

Mail, Notes, iPod and Calendar also have their own integrated search interface (seen in the shots below, which are flanking the new home screen). If the mail search doesn't turn up any results from messages stored on your iPhone, it will move on to search messages still located on your mail server.

via appleinsider