Answer:

After consulting with another tech and further reading, I think this is the best way to set up (create) a general mailbox or virtual and a flex button for the mailbox.

Using the Web GUI to create a VMAILBOX Flex Button

Assuming you are setting the default VM Group *440 and VMID number defaulting the station number (ref: PGM 127 Station Default VM attributes)
I think defaulting the VMID number to the station will not allow [Call Back] to select another Mailbox to manage. Therefore creating a VMAILBOX flex button makes it easy

1. Station Data>Flex Buttons

2. Destination Type>Programing Numbering Plan>Input>*440{stationNumber}
a. Station Number can be any station number in your numbering plan.
i. in my case it was 200 -> *440200
b. <Click> [Save] ->
c. VALUE is display as Multi-VM *440(200)

Note: You can use the flex button to access the VM for the virtual station just like [Call Back] to set up the Mailbox message and manage the messages received. The button led will light red and blink when a message is left.

3. Option: Cascade Mailbox (1-5) in PGM 127 you can set the VM Forward Option to MOVE (move to another station's MB and delete) or COPY (copy to another station's MB) setting the target to one of the Cascade Mailboxes.

In my case I decided not to utilize the cascade feature forcing the user to log into the mailbox and manage because I am using the VMAILBOX flex button.

Did I leave anything out? I could have.