For the moment, we are using the existing address-book, although adding extra rows could be necessary for some purposes. It proved to be too complex to rewrite the entire data model.<p>
Creating a group (e.g. 'allusers') of a (possibly self-defined) group type, adding the address book module and the users who may use it (or allowing them to sign up themselves) is the way to go. In this example, the address-book will be accessible through http://mydomain.com/groups/allusers/address-book.
(This may sound logical and straightforward but in some cases it takes time before someone gets accustomed to ACS-style group administration...)
