This post will specifically guide you, step by step, to be able to get your Google based calendar on your iPhone (with OS3.0+). The calendar app on the iPhone will be the default app, nothing additional you’ll need from the app store.

I will create another post to show you how to add other calendars to your iPhone, e.g. your spouse’s or your kid’s calendars.

1. first, you’ll need your email address… which would be something like “myemail@gmail.com”
   or “myemail@mysuperdomain.com” if you are on Google Apps
2. next, you’ll need to compose your own “server string”… it looks something like this
   https://www.google.com:443/calendar/dav/myemail@gmail.com/user
3. pretty much just simply replace the section “myemail@gmail.com” with your Google based email address, be it with “gmail.com” or “whatever.com”
4. If you’ve got email setup on your iPhone already, you can just email the “Server string” to yourself, which you can copy and paste later… or just type it out carefully on the phone
5. next, pick up your iPhone,  go into “Settings” -> “Mail, Contacts, Calendars” -> “Add Account…” -> “Other” -> “Add CalDAV Account”
6. here’s what you put in
   Server : paste or slowly thumb in the “server string” from above (customized with your own email address of course). When you move to the next field, it’s normal for the “server” to only show “www.google.com”, so don’t worry about it.
   User Name : your full email address, e.g. “myemail@whateverdomain.com”
   Password : the password to the account you put in above
   Description : what ever you’d like to call it, doesn’t matter what you put, it’s for your own identification
7. click “next” when done
8. If all went well, you’ll be taken back to the “Mail, Contacts, Calendars” screen… if you had a typo in the “Server”, “User Name” or “Password” field.. then you’ll be stuck here. Just fix the typo and try again
9. Validation…. Launch the “Calendar” app
10. check and see if your calendar items are showing up, or if you have multiple calendars and it’s hard to validate you can select to see only one calendar
11. in the “Calendar” app, on the top left, tap the “Calendars” button
12. you’ll be presented with the list of Calendars you have configured, select the one you want to check
13. You should now see only the entries belonging to that calendar

have fun =)