Need to check your calendar on the go? Well if you use Google Calendar you’ll be able to check on your events and maintain your schedule from your mobile handset via WAP. The good folks at the Google Calendar team have realized that more people have mobile phones than computers, and now you can visit calendar.google.com from your phone to get see what you have planned. It works just like the Web version so you can see details such as date, time, location, description and guest list.
Calendar for mobile devices [Via Official Google Blog]
Conversely, you can just go to goosync.com.
But when using Google Apps for your Domain, URL is so complicated to type on a mobile as calendar.yourdomain.com/m is not working. In fact, you must use http://www.google.com/calendar/hosted/yourdomain.com/m :(