Google Wave, a real-time collaboration and communication tool, is now partially available on the iPhone. Google Wave is still in the "preview" phase and not without bugs, but if you have an account and have received an invite you can log into your Wave account through Safari.
Google Wave is still very limited, from the homepage:
"Even though you have a Gmail or a Google account, you must be invited to Google Wave in order to sign in. If you haven't been invited by a friend, you won't be able to use the service at this time."
There is a link to "request an invitation" to join Google Wave, which sounds pretentious, but necessary if you want in on the part Google Documents, part Google Chat action. Google Wave merges e-mail, wiki pages, instant messaging, social networking, Reader, and other Google tools.
To use Google Wave, tap on Safari and go to wave.google.com. You will receive a warning saying you're not using a supported browser, but it should still work. You can save the Safari page to your Springboard and launch Wave like an app, too. As of now there is no word on an actual Google Wave app, but I wouldn't be surprised to see one in the App Store.
