We have this scenario:
When we make an outgoing call, for example, to a mobile phone that is turned off, we can't hear the "Early Media" message which informs that the call will be forwarded to the voice mail. We only hear the actual voice mail greeting.
Hard to tell from this little info but all portions must support early media (they should here)
and PRACK should be enabled in CUCM:
With early media cut through, a greeting gets played to the caller before the called party is alerted about the call. Trunks and gateways must support early media cut through for the greeting to get played in such a way. Cisco PRI/MGCP gateways, H.323 gateways and trunks support early media cut through. For SIP trunk to support early media cut through, you must enable PRACK. Be aware that a greeting may not get played if the device does not support early media cut through.