If we have 7931 phones (where it is not recommended to have multiple calls on the same line) can we configure a second extension and have both go to same voicemail subscriber?

example

extension 1 = 1010 (which is subscribers extension in Unity Connection).

Extension 2 = 2010 (which is alternate extension Unity Connection for main ext 1010)

If person is busy on first line 1010, call forwards to second line then if no answer on second line 2010 it goes to voicemail (1010 voicemail box)

If person is not busy, but does not answer first line 1010, call goes to VM and does not rollover to second extension

your help is appreciated.