Update: While researching this problem, I came across a document that talked about enabling the DPNSS feature called: EARLY_TX_CHAN_CONN. Our feature was disabled and after enabling it, 3 party conference calling capabilities went from 0 percent completion to between 33 & 50 percent completion. This feature also fixed MOH issue between our Mitel Desk phone and MS communicator soft phones. Definitely a step in the right direction, but still need help bumping up our 3 party call percentage rate.