1. Make sure you've enabled IMAP in your main Gmail settings
2. On your iPhone or iPod touch's home screen, tap Settings
3. Tap Mail
4. Tap Add Account...
5. Tap Other
6. Tap Add Mail Account
7. Enter your account information, being sure to use your full Gmail address (or full Google Apps email address)
8. Tap Save
9. For Incoming Mail Server:
◦ Host Name is 'imap.gmail.com'
◦ User Name is your full Gmail address, including '@gmail.com' (or full Google Apps email address)
10. For Outgoing Mail Server:
◦ Host Name is 'smtp.gmail.com'
◦ User Name is your full Gmail address, including '@gmail.com' (or full Google Apps email address)
11. Tap Save