If you port that TMO # to GV, then YES, GV can handle call management, including VM. For the record, GV refers to the "disposable carriers cell #" as one of your "forwarding phones". I like the more accurate first name, myself.
On your GV page, under 'settings', 'calls', the 'Caller ID (outgoing)' section determines the behavior you have for texts:
* When I text a Google Voice number from one of my forwarding phones:
1) Don't change anything
OR
2) Display my Google Voice number
It also adds this note: "this setting currently only applies to text messages; calls will be included soon."
However, it's shown that same message for a few years now, I think....
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