iPhoneChat is the latest iPhone-aimed web applications that we should expect to come out for Apple's iPhone.
iPhoneChat allows you to log into your iChat/AIM instant messaging account with buddy list support.
Use your mouse to flick (drag and release) your buddy list up and down like you're supposed to on the iPhone. Click a buddy to start a conversation. You can open multiple conversations... flick left/right to change conversations.
As an early version, it has some limitations, but does offer an good example of what might be possible with iPhone web-apps.