I have received a couple of request of what features work when you connect your Lync 2013 client to an OCS 2007 R2 infrastructure. Here is a list of the features I have tested. This is not an official list, it is just my personal testing.
- IM chat between internal receipients (im to other OCS users in the organization)
- IM chat to external parties (im to federated partners)
- Screen Sharing with internal and external recipients.
- Presence indicator in Outlook 2010 and Outlook 2013
- Presence indicator in SharePoint 2007 and 2010
- VoIP calls between OCS 2007 R2 client and Lync 2010 or Lync 2013 clients
As I mention this is not an official list. If you have other testing scenarios and you are succesfull share your findings and I will update this list.