Google has just launched a mobile version of Google Calendar, which is supposed to load for those visiting the Google Calendar site with a mobile phone. Google describes it more in a blog post today. It appears to work on a range of phones, including Windows Mobile.
As I said on my blog:
This is part of a larger, holistic push in mobile for Google that includes voice search/directory assistance (Goog411), WAP, applications and text messaging. Gmail is also available for mobile.
Google Calendar is also a local events database (which will become important on the phone), though not as fully developed in that regard as a true events database such as Zvents, Attendio or Eventful.
Expect Google to continue to roll out mobile versions of its Internet products and applications, including, I would imagine at some near-term-future point, iGoogle.
Note that Yahoo Calendar is also available on mobile phones.