IPhone – How to set up Gmail on the iPhone 4S with Exchange

This worked for me

Assuming you have already setup the alternate account in your gmail

• Remove the gmail account from your iphone
• Add new mail account
  
  • Settings > Mail > Add Account > Other
  • Enter standard gmail id and password in New Account screen
  • Enter standard gmail id and password in IMAP and SMTP screens (imap.gmail.com, smtp.gmail.com)
  • After account is setup, under "IMAP Account Information" change address field to the desired account (Note that the "Incoming Mail Server" settings will remain as gmail info, this is the difference between creating the account manually and using the automatic gmail setup)

Enjoy

Keyboard shortcuts: Mail has it's own keyboard shortcuts, which you may have to learn.

Alternate email addresses/multiple accounts: works fine. Don't know about plus-addresses.

Priority inbox: this is not supported. Labels work, as does flagging. Public calendars work in iCal.

Syncing is very easy to set up - via IMAP in Mail, and in Preferences in iCal. In Lion it's even simpler.

Yes, you add each account separately in mail. You can still visit them in any browser or device.