I originally posted instructions for configuring an iPhone 2.0 device to an Exchange server back when the iPhone 3G was originally released. While those instructions still hold for the most part, the iPhone interface has changed somewhat, so here’s an updated post with pics for connecting the iPhone 3.x OS to an Exchange server.

1. From the Home screen (unless you’ve relocated the icon) open the Settings app.
2. Click the Mail, Contacts, Calendars item in the list.
   
3. Click Add Account.
   
4. Click Microsoft Exchange at the top of the list.
   
5. Enter your e-mail account information.
   
   For the Email field, enter your default e-mail address exactly as it appears on your outgoing messages. This is important: if your outgoing e-mail address is Jon.Dough@smallbizco.net, you must match it exactly. If you enter jon.dough@smallbizco.net, you may encounter issues with calendar items. You may not need to enter the Domain field, but do enter it if you know what it is. Your username and password should match what you enter to access Outlook Web Access or your network account. If you do not know this information, you will need to get it from your system administrator.
6. Once you have entered the account information, click Next. The iPhone will attempt to connect to your mail server. You may be prompted to enter the name of the mail server if it could not be found automatically. This is the same as the server you use to access Outlook Web Access. If your Outlook Web Access server is https://remote.smallbizco.net/owa, then you need to enter remote.smallbizco.net as the mail server. Then click Next.
   
7. If the iPhone cannot correctly validate the security certificate on your mail server (this may be the case if your Exchange server is running on Small Business Server 2003 or 2008), you will be asked what to do about the connection. If you know you have entered the correct information about your mail server, click Accept. If not, click Cancel.
   
8. Choose which items from the Exchange server you want to sync with your iPhone. If you already have your contacts or calendar synchronizing with another source, you may want to hold off on selecting those to avoid a potential loss of data.
   
9. Click Done when finished.

The iPhone will now start the initial connection to the Exchange server and synchronize the selected information.