Om points to a new mobile version of the 30Boxes web calendar. They've done a very nice job mapping their features to the tiny screen. From the 30Boxes blog:
We now have a full-fledged mobile version of 30 Boxes and we encourage you to try it out. From any wireless phone point your browser to http://m.30boxes.com and login. You have quick access to your schedule, to do lists, and your buddies.
It’s easy to look up an appointment, stay up to date with friends, and even email or sms them from their mobile buddy page.
Nice work. It loads fast on my Treo and entering new events is easy as can be. It's not an easy proposition mapping a rich application interface to the tiny screen and some good thought has obviously gone into this effort.