We are a small business of approximately 25 staff.  We use a mix of Office 2010 and Office 2013 on desktops to connect to our Office 365 accounts.  I am trying to find out if it is possible for all staff to use the same unified Contacts List (Address Book).  I realize that this is normally the function of CRM software, but would like to know if it is possible using just Office or a 3rd party add on.  Research on the web has no been that enlightening!  Any help or pointers would be appreciated.  Best regards, Richard.

Since you are using Office 365 for Business, you can create Contacts in your Global Address List via the Exchange Admin Center.

Another way to go would be to create a shared mailbox to store the contacts in.