This instruction applies to iPhone firmware 3.0 only:

Step 1 – Go to Settings

Step 2 – Tap Mail, Contacts, Calendars

Step 3 – Tap Add Account

Step 4 – Select Microsoft Exchange

Step 5 – In the Email field, enter your full GMail address (name@gmail.com)

Step 6 – Leave the Domain field blank

Step 7 – Username is your full GMail account

Step 8 – Password is your GMail password….duhhh!

Step 9 – Tap Next at the very top (choose Accept if the Unable to Verify Certificate dialog appears)

Step 10 -  You will see a field called Server, enter m.google.com

Step 11 – Tap Next at the very top

Step 12 – Select the Google services you want to sync. Currently only Contacts and Calendar are supported

Step 13 – Unless you want to delete all the existing Contacts and Calendars on your phone, select the Keep on my iPhone option when prompted. This will also allow you to keep syncing with your computer via iTunes.

Step 14 – REJOICE!!!

Google Sync is now set 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.