The Google blog points out the major features of this new client:
- Take a photo on your phone and upload it right to your Orkut album.
- Share photos with orkut friends or SMS the photos to phone contacts not yet on Orkut.
- Call or SMS any of your Orkut friends or phone contacts without leaving the app.
- View scraps, updates from friends, and photo albums in offline mode.
It's a free application, much like Google Maps and Gmail on the mobile; and the installation method is a matter of pointing your smartphone's web browser to m.google.com/orkut.
More at the Official Google Mobile Blog.