The 7985 is a Skinny (SCCP) device, like any other Skinny IP Phone. If you want to use the 'Confrn' and 'MeetMe' keys to create ad-hoc conferences, then the MCU needs SCCP ports registered to CallManager, and the MCU needs to be specified as the first device in the 7985's MRGL (the same is true for IP Phones with VTA attached). However, a SCCP-only MCU will allow SCCP endpoints to dial out to and add H.323 endpoints to conferences, but H.323 endpoints will not be able to initiate conferences (they don't have the softkeys).
You may wish to consider using an H.323 MCU, but all endpoints (SCCP and H.323) will have to dial Conference numbers to join conferences. The IP/VC 3544 MCU allows individual ports to be assigned for use by either SCCP or H.323 (rather than having an all-SCCP or an all-H.323 MCU).
H.323 endpoints can be added as devices in CallManager directly (and assigned a DN), or they can be registered to a Gatekeeper (which can be useful for DHCP-addressed clients), and then an H.225 intercluster trunk (and appropriate route pattern) is configured between the CallManager cluster and the Gatekeeper.
There is more information in the Voice and Video SRND for CallManager:
http://www.cisco.com/warp/public/779/largeent/it/ese/unifiedCommunications.html
