this is an extension of the iPhone Calendar how-tos… in this post, I’ll describe the steps you need to perform to add someone else’s Google calendar to your iPhone Calendar app.

If you just want to add your own calendar, you may skip this and go to this post instead.

Now, the steps to add someone else’s calendar is very similar to add your own using the CalDAV method. The only thing that needs to be done prior to the config in the iPhone is that this person must first share the calendar with you.

I’m not going to re-invent the wheel here, so please follow Google’s Instructions on how to share your calendar. I discourage you from making your personal calendar public. To learn more, read another Google’s FAQ entry.

For the calendar to work, so that you can see something on the iPhone, you need to set the permission level to at least “See all event details”. If it’s set to “See only free/busy (hide details)”, you will be able to add the calendar via CalDAV, but nothing will show up in your calendar. If you are allowed to make changes even, then by all means go and set the permission to “Make changes to events”.  The ultimate you-have-it-all permission will be “Make changes AND manage sharing”, which I would think most people would not need.

If you are using Google Apps, and you can’t share beyond “only see free/busy information”, you’ll need to request your Administrator to increase the level of sharing allowed. This Google FAQ entry should help. *NOTE* after the administrator makes the changes, it will take a while before the system is updated and you can increase the level of detail to be shared on your calendar. This worked within 10mins during my testing.

Now, once the sharing is enabled, you can do a quick validation via your Gmail Calendar. See if the other person’s calendar is now showing up in your account as well. If yes, and you are not seeing “free/busy” information only, you are good.

The final step is to add the calendar to your iPhone’s setup. The steps are exactly the same as adding your own calendar via CalDAV (read this post), except in step 3, instead of using your own email address, you use the address of the person who had shared it with you. Follow through the rest of the steps, using your own Gmail login credentials, and you should be set!

At this point, your calendar should now show your own and the new calendar that was shared with you.

An additional tip for you… now that you have multiple entries from different calendars, it will be helpful to be able to visually identify easily which entries belongs to who. Fortunately, there’s a way to do this, but you’ll have to do this in Gmail Calendar’s web interface.

This is a very simple process, first just login to you Gmail Calendar. Next, on the left column of the page, find the calendar that you can see, and click on the little triangle next to it. A box will pop up and it will have several colors for your to choose from. Select the one you like and it’s done. In the iPhone Calendar, all entries belonging to that calendar will now have the color code you just picked.