I was able to synchronize my Gmail contact & Calendar to my iPhone from using third party web app NuevaSync . Since today, Google has just released Google Sync for iphone to perform the same function. I believe most of my iPhone buddy would want to know how, here’s the step by step showing how to setup your iPhone.

Google Mobile Sync for iPhone

Requirements and Back Up

1. Make sure your device has version 2.2 firmware or above. You can check your current version by going to Settings> About > Version.
To upgrade, follow the instructions at http://www.apple.com/iphone/softwareupdate/.

2. Back up any Contacts and Calendars from your phone to your computer before proceeding. The iPhone will delete Contacts and Calendars during setup.
Learn how to backup your Contacts with iTunes: PC Users - Mac Users.

Getting Started

1. Open the Settings application on your device’s home screen.
2. Open Mail, Contacts, Calendars.
3. Tap Add Account….
4. Select Microsoft Exchange.

Enter Account Info

5. In the Email field, enter the name of the account (anything you’d like).
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.
9. Tap Next at the top of your screen.
10. A new Server field will appear. Enter m.google.com.
11. Press Next at the top of your screen again.

12. Select the Google services you want to sync. Currently only Contacts and Calendar are supported.
Make sure that you have backed up your data before proceeding.

13. Press Sync twice when warned about data loss.

You’ve set up Google Sync for your iPhone. Synchronization will begin automatically if you have Push enabled on your phone. You can also open the Calendar or Contacts app and wait a few seconds to start a sync.

From Google Help

Here’s few good things I’ve found synchronize your iPhone with Google Calendar & Contact

• Calendar – Multi calendar support with different color
• Contact -  Combine Webmail and Mobile contact list, easy to use and share contact information.