A very simple way to share your calendars across multiple macs and your iphone or ipad is to use Google calendar. The Google calender service is the easiest and most flexible free shared calendar service that I’ve found. Here’s how to set it up on a macintosh computer.
1. START A GOOGLE CALENDAR.
Go to google.com, and if you don’t already have one, create a gmail account. (Even if don’t need to use gmail for email you still need to create a gmail account to sync your calendars using Google.)
Login to your gmail account, and select MORE – CALENDAR to start your own google calendar.
That’s it. Press the create button and your gmail calendar will show up in ical. You can edit it, make changes, and it will automatically sync from google to ical.
NOTE: This only works in Snow Leopard. With Snow Leopard syncing a gmail calendar is built into ical and it’s dead easy. (See here for how to do it in Leopard, and this post for Google’s pre-leopard work-around. )
NOTE: How to share calendars as read-only. the above method will completely sync your information both ways. Any information edited on one computer will automatically copy across to the others. If you want the sharing to be one way only (for example to share a calendar with a friend but so that they cannot edit it, simply proceed as above on your computer, but then go into gmail, calendar settings, and get the calendar URL. Copy the URL and in your friends ical select ‘Calendar’ and ‘Subscribe to Calendar’ and paste in the URL. This will allow them to see your calendar but not edit it.
See here for how to sync your Address book.