The iPhone 4.0 + and iPad 2 use Microsoft Exchange ActiveSync, to push your Mail, Contacts, and Calendar data to your iPhone.
*Note 1 - iPhone OS version 4.0 and later will support multiple ActiveSync accounts. Prior versions of the iOS will only support one ActiveSync account.
*Note 2 - Setting up these instructions will override any Contacts or Calendars already on the device. Please back those up prior to following these steps as they are not recoverable.
1. Setup your Exchange e-mail account by selecting the Settings icon.
2. Select Password & Accounts
3. Select Add Account
4. Select Microsoft Exchange
5. Use the following settings and then select Next.
Domain: (leave blank)
User Name: email@example.com
Password: (your password)
6. Select what you would like to sync to the iPhone and then press Done.