This article shows an example of results on the iPhone 3.0 after synchronizing with a mailbox that has a complex subfolder structure.
This screenshot shows an example folder structure in Outlook:
Under Mail on iPhone you can see all the mail folders, including subfolders (such as Inbox > Personal) and other folders on the same level as the Inbox (such as Inbox for AOL emails). Folders are displayed in a tree view, and subfolders appear under the parent folder, exactly as in Outlook. You may see the content of each folder by simply tapping it once.
Under Calendar on the iPhone, you can see all the calendar folders and subfolders in one list. Each calendar has its own color. You can choose to view one calendar, or events from all calendars. To view events from all calendars, tap All. You will see appointments displayed in the color that corresponds to each folder's individual color.
Similarly to calendars, the Contacts application syncs all the folders and subfolders and shows them all in one list. Clicking on All Contacts shows all the contacts from all folders and subfolders in one list. It is possible that this functionality (synchronization of contact subfolders) is broken in the 3.1 update.
If you click the email address right below the Groups label (in the screenshot above, this is test123@...), you can perform a lookup in the company address book (Global Address List, or GAL).