calendaring

A client of a client has problems with Outlook and they are looking at moving to different software. A basic Postfix/Dovecot installation does everything they need for email but the issue is calendaring. They want "shared diaries" with Outlook clients and phones, I think mainly iPhone. What is involved in setting this up? Apache has built in WebDAV support, what else do I need? -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/