Mirror?
 

Don't know where to put this, so I shall try it here. I have an "07 2LT, with the self-dimming interior mirror with integral compass. Works fine. I was gifted another mirror; this one with additional buttons for On Star. Are the electronics for On Star integral with the mirror or are they in the chassis? I guess the question really is: if I mount and plug in this mirror, will I have ( if I set up the subscription and pay the fees) access to On Star?

No, the OnStar module is not in your car.
I have the same mirror, OnStar, Autodimming, Bluetooth to a cell phone, compass.
the Bluetooth doesn’t work either.
The autodim and compass are a nice feature.

OldSwede GM did offer Onstar as an add on package to cars that are not equipped. I think I saw it offered at Best Buy. I am not sure if it is still available.

Crutchfield had a kit, but I think it’s obsolete.

https://www.crutchfield.com/p_293FMV/OnStar-FMV.html

I get an occassional email form "big brother" (GM) asking why my hhr is not "talking" (onstar inactive) Can the government track my travels since they owned the company during my production date? My mirror has the onstar stock auto dim.

I haven't bothered to get labor operation R4481 done since my battery discharged as I am waiting for my tires to wear out and do TPMS at same time. I'm sure that's why the emails are sent. I suppose the airbag deployed notice wouldn't be sent in an accident either?