Business Contact Manager for Outlook 2003 Update links with Microsoft Small
Business Accounting 2006. It could also link to other applications, if there
is a need by the external vendors to do so.
Business Contact Manager for Outlook 2007 handles interfacing with external
applications differently -- by allowing the external application to initiate
the integration and decide the depth of integration.
There are public data views available to external apps, and APIs available
to external apps.
Any application can use these APIs and access public data views, whether the
applications are from Microsoft or other third parties -- in the US or in any
of the other available countries BCM is available in.
So, to directly answer your question -- if Quickbooks (or rather Intuit)
wants to interface to Business Contact Manager for Outlook 2007 and take
advantage of these new capabilities, they just have to provide this
functionality to its customers.
I imagine there will soon be lots of partners developing vertical
customizations, and interfaces to BCM using the public APIs and public data
views.