I was working in an environment that had Cisco CM and Lync 2013 both using Exchange 2013 UM as the voice mail platform. The Exchange 2013 had been migrated from Exchange 2010 and no the Tel URI dial plan was no longer functional. So Cisco Phone users would hear a fast busy when they called the voice mail hunt group pilot identifier number.
I ran SIP trace on the Cisco gateway and saw that the Exchange UM server was responding with a "302 Moved Temporarily" message to the SIP INVITE. I also noticed that the Exchange UM services was attempting to redirect the connection to the UMWorker process on TCP port 5065. Therefore, I changed the session target port from 5062 (I had changed it from 5060 to 5062 since the EAC has UM on the mailbox server defined with that port) to 5065. After making this change, voice mail for Cisco phones was working again. Here is an example of how the dial-peer is configured:
dial-peer voice 1014 voip
description *Exchange 2013 Unified Messaging*
translation-profile outgoing LYNC_ADD_PLUS
session protocol sipv2
session target ipv4:10.1.20.36:5065
session transport tcp
incoming called-number .
fax rate disable
fax protocol pass-through g711ulaw