I am working with a client who is using Cisco CUCM with Cisco Phones, along with Microsoft Exchange 2010 voice mail on the UM , but when you divert the phone to voicemail you are not prompted with the users voicemail prompt – you are prompted with the Subscriber access greeting of “ Welcome , you are connected to Microsoft exchange ,…etc )
Usually when you call someone and there is no answer then you are transferred to the Pilot number, the extension of the person you are calling is sent also in the request so that you would be directly transferred to the users voice mail not to the Welcome greeting.
This Problem Happens when Diverted Calls are not accepted because both sides cannot agree on DTMF handling , the MTP is important, because it deals with differences in how DTMF is signaled between the phones and gateways and the sip trunk
Just make sure the following on the Cisco SIP trunk:
1- Media Termination Point Required "Enabled"
2- Redirecting Diversion Header Delivery "Enabled"