Unified Messaging requires that you integrate Exchange Server 2010 with the existing telephony system for your organization. A successful deployment requires you to make a careful analysis of your telephony infrastructure. Although Exchange Server 2007 and Exchange Server 2010 UM have almost identical architecture Yet IP-PBX supported integration has changed with Exchange Server 2010/Exchange Server 2010 SP1. For e.g. Exchange Server 2010 SP1 only support Cisco IP BPX with Call manager 5.0, 5.1, 6.0 and 7 as direct SIP Integration (without use of IP Gateway).
The article below explains in details the different Integration types between Exchange Server 2010 (SP1) Unified Messaging and Telephony BPX Infrastructure :
More Details: Telephony Advisor for Exchange 2010