Your iPhone 3g is probably using HTTP for access, the same thing as MS
Internet Explorer, or Mozilla Firefox. MS Outlook does not use HTTP, it uses
either POP3 (which Yahoo! Mail Plus uses; 'at&t Yahoo! HSI' offers "Mail
Plus" capability to AT&T DSL customers), or IMAP (which Yahoo! does not
use). You will always see all of your folders with an HTTP application, but
you will only ever access the Inbox with a POP3 application.
The technology is there, to synchronize your Yahoo! account folders with MS
Outlook; if only Yahoo! would actually implement it: IMAP. Many have
requested it of Yahoo!; so far, Yahoo! has been resistant to those requests.
~Oh Lord, why have you come
~To Konnyu, with the Lion and the Drum