we are in the process of migrating exchange 2007 to 2013 (also have ex2010 as intermediate as you cannot jump directly from 2007 to 2013). i have tested the unity con with 2013. as cisco supports ex2013 and documented how the service account and all should be created. it works fine with ex2013 and ex2010. it is able to find the mailbox in 2013 and 2010.
the only problem is that if we have a mailbox in 2007, the unity conn is not able to find mailboxes located in 2007 via ex2013. the connection pops out this error msg
"The server to which the application is connected cannot impersonate the requested user due to insufficient permission"
according to theory, the service account created to support ex2013 should be able to locate mailboxes located in 2013, 2007, and 2010 witout issues.
i have the modified the same service account and added permissions as if it was created to support 2007. but no luck.