I've gone through the setup about a billion times (at least that's what it feels like) - but I've never been able to successfully have Exchange 2013 UM answer any phone calls to either the mailbox service or any configured auto-attendant.
To make sure I wasn't crazy, I have reinstalled Exchange 2010 in a 100% identical configuration, and she answers with absolutely no problems what-so-ever. Users are led to their mailbox, the autoattendent routes calls accordingly, etc.
. . . But moving back into a 2013 environment, in a 100% identical configuration, the server itself never actually answers any of the calls.
Would anybody happen to have any ideas on where I could go to check out the issues here?