Steps to share Public Folder Contacts in Exchange 2010:
Log on in the EMS, Open the Public Folder Management Console and Create a Top-Level Public Folder in Exchange Server.
Assign client permissions on the Public Folder using Add-publicFolderClientPermission command in EMS. You must give the user, who will create a subfolder in this public folder using outlook, at least Publishing Author permission,
Now login to oultook using the credentials of the user whom u gave permission on the public folder. Goto public folders and Create a sub public folder under the Public Folder u created in exchang using Microsoft Outlook as a “Contact public folder”.
In order to set up the subfolder as a Shared Contacts, you will need to assign client permissions on the contacts public folder to the users of your choice using Add-PublicFolderClientPermission command. You can also use “Remove-PublicFolderClientPermission” to remove client permissions from the contacts public folder.