How to Set Up Push Gmail on the iPhone - Enter Your Gmail Account Details

In the "Email" field, type in your full Gmail address.
Leave the "Domain" field blank.
In the "Username" field, enter your full Gmail address again.
In the "Password" field, enter your account password.
The "Description" field may say "Exchange" or it may be filled in with your e-mail address; you can change this to something else if you like. (This is the name that you'll use to identify this account when you access the iPhone's e-mail app.)
Note: If you already have your iPhone setup to check this Gmail account (not using the Google Sync feature), you are creating a duplicate e-mail account. You can delete the other account either before or after you add this one, as you don't need two versions of the same e-mail account setup on your phone.
Tap "Next."
You may see a message that says "Unable to Verify Certificate." If you do, tap "Accept."
A new field, called "Server," will appear on the screen. Enter m.google.com.
Tap "Next."