the description is a little messy but if i understand correctly there is nothing wrong, the default behavior is that the VM box is selected using the original called party number.

Route Forwarded Calls by the First or Last Redirecting Number

Cisco Unity supports the option of routing calls based on either the first or last redirecting number when a call is forwarded to Cisco Unity.

Note the following:

This option requires Cisco Unity-CM TSP 8.1(2) or later.

This option is not supported by integrations through PIMG units.

This option can be changed through the Advanced Settings Tool (AST), which is available in Tools Depot.

http://www.cisco.com/en/US/docs/voice_ip_comm/unity/5x/release/notes/501curelnotes.html#wp507371

Call Information Exchanged by the Phone System and Cisco Unity

The phone system and Cisco Unity exchange call information to manage calls and to make the integration features possible. With each call, the following call information is typically passed between the phone system and Cisco Unity:

•The extension of the called party.

•The extension of the calling party (for internal calls) or the phone number of the calling party (if it is an external call and the phone system supports caller ID).

•The reason for the forward (the extension is busy, does not answer, or is set to forward all calls). There is also a reason code for Direct Calls.

Cisco Unified Communications Manager SCCP and SIP trunk integrations can also provide the following call information (the choice of first and last redirecting number is set in the Advanced Settings Tool, which is available in Tools Depot):

•Called number

•First redirecting number

•Last redirecting number

Note Cisco Unity can use either the first redirecting number or last redirecting number, depending on the setting in the Advanced Settings Tool, which is available in Tools Depot.

http://www.cisco.com/en/US/docs/voice_ip_comm/unity/5x/design/guide/5xcudg060.html#wp1040786

you need unity 5.x for the above

HTH

java

if this helps, please rate