The iPhone is really easy to set up. I don’t particularly like the onscreen keyboard input or the lack of cut and paste (edit: fixed in OS v3.0), but it is really easy to set up a connection to Exchange.
All you need is:
email address – This is the email address of the user
domain – Leave this blank in most cases
username – the username for logging into the domain
password – the user’s password
Click next, and the iPhone will attempt to connect to the server automatically. In most SBS cases, this will fail, and the phone will request a servername.
servername – the FQDN for the domain where Exchange OWA is located. In many SBS2003 installations, this is typically mail.domain.com. On SBS2008, this will normally be remote.domain.com.
When you are done, the screen should look something like this.