[rkh]

Looking for some "how does it work" info.
Subaru uses a Bluetooth or wired connection for your phone. Does it just connect the microphone/speakers/steering wheel controls? Or does it somehow make use of the fin antenna to boost signal for trans and reception? In other words, aside from hands-free, does my pocket phone perform better when connected to my Subaru than it does by itself?

Datapoint: You can buy and install cell phone signal boosters which require the phone be in proximity to the booster and then uses an external antenna to improve reception.
Datapoint: GM's OnStar uses a permanently installed and separate phone to connect microphones/speakers/controls and the externally mounted antenna. From experience, its a well-performing phone attributable in part to the elimination of the need to be portable, thus it uses the 80 pound 12volt car battery for power and an optimally mounted external antenna to connect to the cell tower. As a phone, its kicka** but has several disadvantages including cost, need for an OnStar subscription and a separate number. But technically and performance, I've used it to make and receive calls in some pretty remote places when no one's pocket phone can get through.

 

[NoData]

Looking for some "how does it work" info.
Subaru uses a Bluetooth or wired connection for your phone. Does it just connect the microphone/speakers/steering wheel controls? Or does it somehow make use of the fin antenna to boost signal for trans and reception? In other words, aside from hands-free, does my pocket phone perform better when connected to my Subaru than it does by itself?

Datapoint: You can buy and install cell phone signal boosters which require the phone be in proximity to the booster and then uses an external antenna to improve reception.
Datapoint: GM's OnStar uses a permanently installed and separate phone to connect microphones/speakers/controls and the externally mounted antenna. From experience, its a well-performing phone attributable in part to the elimination of the need to be portable, thus it uses the 80 pound 12volt car battery for power and an optimally mounted external antenna to connect to the cell tower. As a phone, its kicka** but has several disadvantages including cost, need for an OnStar subscription and a separate number. But technically and performance, I've used it to make and receive calls in some pretty remote places when no one's pocket phone can get through.

I don't know the answer to your questions, but I strongly doubt that connecting your cell phone (by Bluetooth or cable) to the Subaru boosts it's signal.

According to this web site https://www.onstar.com/us/en/plans-pricing.html

Onstar "Our most comprehensive plan keeps you connected, secure and protected": for $349/year you get "30 Hands-free calling Minutes every month" (in addition to other services)

 

[1stsubie]

Looking for some "how does it work" info.
Subaru uses a Bluetooth or wired connection for your phone. Does it just connect the microphone/speakers/steering wheel controls? Or does it somehow make use of the fin antenna to boost signal for trans and reception? In other words, aside from hands-free, does my pocket phone perform better when connected to my Subaru than it does by itself?

Datapoint: You can buy and install cell phone signal boosters which require the phone be in proximity to the booster and then uses an external antenna to improve reception.
Datapoint: GM's OnStar uses a permanently installed and separate phone to connect microphones/speakers/controls and the externally mounted antenna. From experience, its a well-performing phone attributable in part to the elimination of the need to be portable, thus it uses the 80 pound 12volt car battery for power and an optimally mounted external antenna to connect to the cell tower. As a phone, its kicka** but has several disadvantages including cost, need for an OnStar subscription and a separate number. But technically and performance, I've used it to make and receive calls in some pretty remote places when no one's pocket phone can get through.

As an iPhone user, I connect my device via USB to obviously to charge my device for one & also to connect to Apple Carplay for navigation guidance, text messages & calls. My device doesn't perform better when connected. I receive the exact same cell coverage. In regards to GM OnStar, I have no experience with GM vehicles or OnStar & never will.