Google Mobile Blog announces that the interface is available "in 33 new markets and 16 new languages, from Argentina to New Zealand, from Swedish to Chinese". If you have an iPhone, a simple visit to google.com should direct you to the special interface, while allowing you to go back to the "classic" interface. For Google Apps users, the address is a little bit complicated: http://www.google.com/m/a/DOMAIN (for example: http://www.google.com/m/a/google.com).
Google for iPhone packages rich mobile interfaces for Google Search, Gmail, Google Calendar, Google Docs, Google Reader, Picasa Web, Google Notebook and now Google News. Unlike the mobile interfaces offered for other devices, Google shows search suggestions, auto-complete for Gmail contacts, slideshows in Picasa Web and includes a presentation viewer in Google Docs.
I'm sure the plan is to extend the availability of this mobile offering to other high-end phones.
Update: an older iPhone interface is still available at http://www.google.com/m/i and there's also a classic Google homepage at http://www.google.com/m/classic. iGoogle for iPhone can be found at http://www.google.com/ig/i.