As long as ports are properly opened, it should work. TCP port 2000, 2443 (is secure skinny). Audio UDP 16384-32767. You may also want to follow this link.
http://www.cisco.com/en/US/products/ps6120/products_configuration_example09186a008081042c.shtml#configs4
I would say create a wide open rule first make sure every thing works and then start locking it down.
HTH
Sankar
PS: please remember to rate posts!
Sankar Nair
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus