EGW has its own adress book (customer database) that can be shared.
Cyrus-imap also enable folder sharing within mail accounts.
If mobility is needed, a web-based application might be better but if Outlook is a requierement, then the implementation of EGW should be discarded.
Using Outlook *and* EGW is probably not recommended for the time being. It's one or the other, in my opinion. And either way is working very fine.