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.

2. PUT YOUR GOOGLE CALNEDAR INTO ICAL
Go into ical and select ical – preferences.

Now select the ‘Accounts’ Tab, then click the + button to add an account.

Now select ‘Google’ under Account type, and then enter your gmail address and password.

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.

MobileMe doesn’t achieve this. iCal shared calendars via itunes doesn’t achieve this. After much experimenting I found the best way is through Google calendar.

Google calendar allows editing and viewing from iCal on your mac and from your iPhone, plus you can let anyone else edit your calendar if you want them to. So Google calendar becomes the hub. Here’s how it all works:

STEP 1. GET A GOOGLE CALENDAR ACCOUNT.
You can set up a new calendar in Google at http://google.com/calendar

STEP 2. SYNC ICAL WITH GOOGLE.
Google has released a program called calaboration that will automatically put all the settings for your Google calendar into iCal. Download and run calaboration. It looks like this, you just select the calendars you want to add into your iCal account.

STEP 3. SYNC IPHONE WITH GOOGLE

If you have iphone version 3 you can just use the built in CalDAV to access your Google Calendar. Go to Settings then Mail, Contacts, Calendars then Add Account then Other then Add CalDAV Account.
You’ll see a page like this:

Enter the settings for your google account here and that’s it!

NOTE – More than 1 Calendar.
If you have more than one Google Calendar you’d like to sync, you need to copy the URL of the calendar from ical across to your iphone. To do this, AFTER you have used callaboration to put the google settings into ical, go into ical, preferences, Accounts, Server Settings – it looks like this.

You need to type that URL into the ‘Advanced Settings’ – ‘Account URL’ of the Calendar on your iphone. It’s quite a long text so the easiest way is to copy it from ical into mail, mail it to your iphone, copy it out of mail and paste it in.

NOTE 2: Old iphone software.
If you have iphone software version 2 you’ll need to use Nuevasync. You set it up in your iPhone as a Microsoft Exchange server that points to Nuevasync. You can sync directly from google to iphone but all the calendars come across as one calendar. To choose which colors the calendars are on the iphone, you need to enable them one at a time from neuvasync, checking the iphone calendar each time, and they will import into the iphone in order of the following colors: red (first calendar) , orange (2nd) , blue, green then purple. eg the first calendar you enable will be red, and so on.

Well as great as the iphone is, the software is laggign a fair way behind and calendar syncign is one example.

After many hours, here’s a solution I found to sync multiple calendars across different computers, with anyone being able to edit the calendars, and see them on your iphone as well.

1. SET UP A MASTER CALENDAR Your master calendar needs to be in google (not on your mac). So create a google calendar here. Because I wanted to share it among my colleagues and have them edit it, I created a special goggle account just for this calendar. After you create the calendar you can export your existing  events from your mac as an ics file  and import them into google calendar.

2. SYNC IT TO ICAL Download a little google application called ‘Calaboration’ from here which will add your google calendar to ical. You will need to enter your google id and password. You will need to run Calaboration on any mac you want to access the google calendar on.

3. SYNC IT TO IPHONE Your iphone can sync to google calendar via the ClaDAV option on the iphone. Google is basically being an exchange server that your phone syncs to. The instructions are here.

I have a newer post about this here.