Here is how to synchronize your Google Calendar with your iPhone Calendar:
Open the Settings application on your device's home screen
Open Mail, Contacts, Calendars
Tap Add Account
4. Select Microsoft Exchange. iOS 4.0+ allows multiple Exchange accounts
However, if you're on a device that doesn't let you add a second account, you could also use CalDAV to sync Google Calendar and IMAP to sync Gmail.
Enter Account Info.
5. In the Email field, enter your full Google account email address. If you use a @googlemail.com address, you may see an Unable to verify Certificate warning when you proceed to the next step.
6. Leave the Domain field blank
7. Enter your full Google account email address as the Username
8. Enter your Google account password as the Password
(If you are a 2-step Verification User, please use an Application-Specific Password instead.)
9. Click Next at the top of your screen
Choose Cancel if the Unable to Verify Certificate pop-up appears.
10. When the new Server field appears, enter m.google.com
11. Press Next at the top of your screen again
12. Select the Google Services (Mail, Calendar, and Contacts) you want to sync. To receive and respond to meeting requests on your device, both Mail and Calendar need to be turned on and new invitations need to be enabled in your Google Calendar Settings.
To enable new invitations, sign in to your Google Calendar using the web browser on your phone or computer. Go to Calendar Settings > Calendars and click on the Notifications for the calendar you want to sync. Under Email, check New Invitations (and any of the other Invitation Settings you want enabled), then click Save.
13. Unless you want to delete all the existing contacts and calendars on your phone, select the Keep on my iPhone (or iPad or iPod touch) option when prompted. This will also allow you to keep syncing with your computer via iTunes.
If you want to sync only the My Contacts Group, you must choose to Delete Existing Contacts during the Google Sync install when prompted. If you choose to keep existing contacts, it will sync the contents of all contacts group instead. If there are no contacts on your phone, the latter will happen - the contents of your ll Contacts Group will be synced.
Synchronization will begin automatically if you have push enabled on your device. You can also open the Mail, Calendar, or Contacts App and wait a few seconds to start a Sync.
If you decide to sync your Google Calendar via the Google Mail Sync method and have External iCal Calendars set up in your Google Calendar, go to this page and follow instructions: http://support.google.com/mobile/bin/answer.py?hl=en&answer=139206
Please contact firstname.lastname@example.org with any questions.