It could (read at least... not sure about write) be done, theoretically, using PHP and the IMAP functions, and a little bit of coding voodoo and black magic.
Outlook mailboxes can definitely be accessed via IMAP. The contacts however, I'm not so sure of (never tried). But it's a starting point of where to look. 😃
Another possibility: If PHP box is running windows, perhaps there's some Outlook COM object that can be loaded to access the contacts.