I have a client (law firm) where two users want to share contacts.  On the
surface, this would seem like a simple process but these are lawyers, so
nothing is simple.  What they would like to be able to do is:

1)  Share a common contact list
2)  Let it be the default address book for both users

now it gets tough:

3)  Have all the "activities" associated with a particular contact available
from both user accounts AND
4)  Sync the contact list on a Treo 600

Here's what I've tried:  I created a Public Folder Contact List and gave
both users "owner" permissions.  That gets me through items 1 and 2 above.  
On item 3, i'm assuming that because i can't see activities for both that
it's a rights issue; any other ideas?  On item 4, i'm clueless.

Any help would be greatly appreciated.

christel